PROSPECTUS



                                TETRA TECH, INC.

                       144,482 SHARES OF COMMON STOCK

                               ----------------

     The stockholders of Tetra Tech, Inc. listed herein are offering and
selling 144,482 shares of Common Stock of Tetra Tech, Inc. under this
prospectus.

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        INVESTING IN TETRA TECH, INC. COMMON STOCK INVOLVES RISKS.
                SEE "RISK FACTORS" BEGINNING ON PAGE 2.

                               ----------------

     All of the selling stockholders obtained their shares of Common Stock on
June 18, 1999 in connection with Tetra Tech, Inc.'s acquisition of Utilities
& C.C., Inc.  Some or all of the selling stockholders expect to sell their
shares.

     The selling stockholders may offer their shares of Common Stock through
public or private transactions, on or off the Nasdaq National Market, at
prevailing market prices, or at privately negotiated prices.

                               ----------------

     Tetra Tech, Inc. Common Stock is traded on the Nasdaq National Market
under the symbol "WATR."  On October 27, 1999, the closing price of the
Common Stock on the Nasdaq National Market was $16 1/16 per share.

                               ----------------

     THE SECURITIES AND EXCHANGE COMMISSION AND STATE SECURITIES REGULATORS
HAVE NOT APPROVED OR DISAPPROVED THESE SECURITIES, OR DETERMINED IF THIS
PROSPECTUS IS TRUTHFUL OR COMPLETE.  ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                               ----------------

             THE DATE OF THIS PROSPECTUS IS OCTOBER 28, 1999




                                 THE COMPANY

     Tetra Tech, Inc. is a leading provider of specialized management
consulting and technical services in three principal business areas: resource
management, infrastructure and communications.  As a specialized management
consultant, we assist our clients in defining problems and developing
innovative and cost-effective solutions.  Our management consulting services
are complemented by our technical services.  These technical services, which
implement solutions, include research and development, applied science,
engineering and architectural design, construction management, and operations
and maintenance.  Our clients include a diverse base of public and private
organizations located in the United States and internationally.

     Since our initial public offering in December 1991, we have increased
the size and scope of our business and have expanded our service offerings
through a series of strategic acquisitions and internal growth.  We have more
than 3,600 employees worldwide, 3,500 of whom are located in North America in
more than 100 locations.  In addition, we have established a presence in
Asia, South America and Europe.

     Our principal executive offices are located at 670 North Rosemead
Boulevard, Pasadena, California 91107, and our telephone number is (626)
351-4664.  Our website is located at www.tetratech.com.  Information
contained in our website is not a part of this prospectus.

                              USE OF PROCEEDS

     The selling stockholders are offering all of the shares of Common Stock
covered by this prospectus.  We will not receive any proceeds from the sales
of these shares.

                              RISK FACTORS

     AN INVESTMENT IN THE SHARES OF COMMON STOCK OFFERED BY THIS PROSPECTUS
INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD CAREFULLY REVIEW THE FOLLOWING
RISK FACTORS AS WELL AS THE OTHER INFORMATION SET FORTH IN THIS PROSPECTUS
BEFORE MAKING AN INVESTMENT.

     SOME OF THE INFORMATION IN THIS PROSPECTUS OR INCORPORATED BY REFERENCE
IN THIS PROSPECTUS CONTAINS FORWARD-LOOKING STATEMENTS THAT INVOLVE
SUBSTANTIAL RISKS AND UNCERTAINTIES. YOU CAN IDENTIFY THESE STATEMENTS BY
FORWARD-LOOKING WORDS SUCH AS "MAY," "WILL," "EXPECT," "ANTICIPATE,"
"BELIEVE," "ESTIMATE" AND "CONTINUE" OR SIMILAR WORDS. YOU SHOULD READ
STATEMENTS THAT CONTAIN THESE WORDS CAREFULLY BECAUSE THEY: (1) DISCUSS OUR
FUTURE EXPECTATIONS; (2) CONTAIN PROJECTIONS OF OUR FUTURE OPERATING RESULTS
OR OF OUR FUTURE FINANCIAL CONDITION; OR (3) STATE OTHER "FORWARD-LOOKING"
INFORMATION. WE BELIEVE IT IS IMPORTANT TO COMMUNICATE OUR EXPECTATIONS TO
OUR INVESTORS. THERE MAY BE EVENTS IN THE FUTURE, HOWEVER, THAT WE ARE NOT
ACCURATELY ABLE TO PREDICT OR OVER WHICH WE HAVE NO CONTROL. THE RISK FACTORS
LISTED IN THIS SECTION, AS WELL AS ANY CAUTIONARY LANGUAGE IN THIS
PROSPECTUS, PROVIDE EXAMPLES OF RISKS, UNCERTAINTIES AND EVENTS THAT MAY
CAUSE OUR ACTUAL RESULTS TO DIFFER MATERIALLY FROM THE EXPECTATIONS WE
DESCRIBE IN OUR FORWARD-LOOKING STATEMENTS. BEFORE YOU INVEST IN OUR COMMON
STOCK, YOU SHOULD BE AWARE THAT THE OCCURRENCE OF ANY OF THE EVENTS DESCRIBED
IN THESE RISK FACTORS AND ELSEWHERE IN THIS PROSPECTUS COULD HAVE A MATERIAL
ADVERSE EFFECT ON OUR BUSINESS, FINANCIAL CONDITION AND OPERATING RESULTS AND
THAT UPON THE OCCURRENCE OF ANY OF THESE EVENTS, THE TRADING PRICE OF OUR
COMMON STOCK COULD DECLINE AND YOU COULD LOSE ALL OR PART OF YOUR INVESTMENT.

THERE ARE RISKS ASSOCIATED WITH OUR ACQUISITION STRATEGY THAT COULD ADVERSELY
IMPACT OUR BUSINESS AND OPERATING RESULTS

     A significant part of our growth strategy is to acquire other companies
that complement our lines of business or that broaden our geographic
presence. During fiscal 1998, we purchased ten companies in five separate
transactions.  During the nine months ended July 4, 1999, we purchased seven
companies.  We expect to continue to acquire companies as an element of our
growth strategy.  Acquisitions involve certain risks that could cause our
actual growth or operating results to differ from our expectations or the
expectations of security analysts. For example:


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     -  We may not be able to identify suitable acquisition candidates or to
        acquire additional companies on favorable terms;

     -  We compete with others to acquire companies.  We believe that this
        competition will increase and may result in decreased availability or
        increased price for suitable acquisition candidates;

     -  We may not be able to obtain the necessary financing, on favorable
        terms or at all, to finance any of our potential acquisitions;

     -  We may ultimately fail to consummate an acquisition even if we announce
        that we plan to acquire a company;

     -  We may fail to successfully integrate or manage these acquired
        companies due to differences in business backgrounds or corporate
        cultures;

     -  These acquired companies may not perform as we expect;

     -  We may find it difficult to provide a consistent quality of service
        across our geographically diverse operations; and

     -  If we fail to successfully integrate any acquired company, our
        reputation could be damaged. This could make it more difficult to
        market our services or to acquire additional companies in the future.

In addition, our acquisition strategy may divert management's attention away
from our primary service offerings, result in the loss of key clients or
personnel and expose us to unanticipated liabilities.

     Finally, acquired companies that derive a significant portion of their
revenues from the Federal government and that do not follow the same cost
accounting policies and billing procedures as we do may be subject to larger
cost disallowances for greater periods than we typically encounter.  If we
fail to determine the existence of unallowable costs and establish
appropriate reserves in advance of an acquisition we may be exposed to
material unanticipated liabilities, which could have a material adverse
effect on our business.

OUR QUARTERLY OPERATING RESULTS MAY FLUCTUATE SIGNIFICANTLY, WHICH COULD HAVE
A NEGATIVE EFFECT ON THE PRICE OF OUR COMMON STOCK

     Our quarterly revenues, expenses and operating results may fluctuate
significantly because of a number of factors, including:

     -  The seasonality of the spending cycle of our public sector clients,
        notably the Federal government;

     -  Employee hiring and utilization rates;

     -  The number and significance of client engagements commenced and
        completed during a quarter;

     -  Delays incurred in connection with an engagement;

     -  The ability of our clients to terminate engagements without penalties;

     -  The size and scope of engagements;

     -  The timing of expenses incurred for corporate initiatives;

     -  The timing and size of the return on investment capital; and


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     -  General economic and political conditions.

Variations in any of these factors could cause significant fluctuations in
our operating results from quarter to quarter and could result in net losses.

THE VALUE OF OUR COMMON STOCK COULD CONTINUE TO BE VOLATILE

     The trading price of our Common Stock has fluctuated widely.  In
addition, in recent years the stock market has experienced extreme price and
volume fluctuations.  The overall market and the price of our Common Stock
may continue to fluctuate greatly. The trading price of our Common Stock may
be significantly affected by various factors, including:

     -  Quarter to quarter variations in our operating results;

     -  Changes in environmental legislation;

     -  Changes in investors' and analysts' perception of the business risks
        and conditions of our business;

     -  Broader market fluctuations; and

     -  General economic or political conditions.

IF WE ARE NOT ABLE TO SUCCESSFULLY MANAGE OUR GROWTH STRATEGY, OUR BUSINESS
AND RESULTS OF OPERATIONS MAY BE ADVERSELY AFFECTED

     We are growing rapidly. Our growth presents numerous managerial,
administrative, operational and other challenges. Our ability to manage the
growth of our operations will require us to continue to improve our
operational, financial and human resource management information systems and
our other internal systems and controls. In addition, our growth will
increase our need to attract, develop, motivate and retain both our
management and professional employees. The inability of our management to
manage our growth effectively or the inability of our employees to achieve
anticipated performance or utilization levels, could have a material adverse
effect on our business.

THE LOSS OF KEY PERSONNEL OR OUR INABILITY TO ATTRACT AND RETAIN QUALIFIED
PERSONNEL COULD SIGNIFICANTLY DISRUPT OUR BUSINESS

     We depend upon the efforts and skills of our executive officers, senior
managers and consultants.  With limited exceptions, we do not have employment
agreements with any of these individuals.  The loss of the services of any of
these key personnel could adversely affect our business. Although we have
obtained non-compete agreements from certain principals and stockholders of
companies we have acquired, we generally do not have non-compete or
employment agreements with key employees who were not once equity holders of
these companies.  We do not maintain key-man life insurance policies on any
of our executive officers or senior managers.

     Our future growth and success depends on our ability to attract and
retain qualified scientists and engineers.  The market for these
professionals is competitive and we may not be able to attract and retain
such professionals.

CHANGES IN EXISTING LAWS AND REGULATIONS COULD REDUCE THE DEMAND FOR OUR
SERVICES

     A significant amount of our resource management business is generated
either directly or indirectly as a result of existing Federal and state
governmental laws, regulations and programs. Any changes in these laws or
regulations that reduce funding or affect the sponsorship of these programs
could reduce the demand for our services and could have a material adverse
effect on our business.


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OUR REVENUES FROM AGENCIES OF THE FEDERAL GOVERNMENT ARE CONCENTRATED, AND A
REDUCTION IN SPENDING BY THESE AGENCIES COULD ADVERSELY AFFECT OUR BUSINESS
AND OPERATING RESULTS

     Agencies of the Federal government are among our most significant
clients.  During fiscal 1998 and the nine months ended July 4, 1999,
approximately 46.8% and 39.6%, respectively, of our net revenue was derived
from three Federal agencies as follows: 26.2% and 22.2%, respectively, of our
net revenue was derived from the Department of Defense (DOD), 17.1% and
12.5%, respectively, from the Environmental Protection Agency (EPA), and 3.5%
and 2.9%, respectively, from the Department of Energy (DOE).  Some of our
contracts with Federal government agencies require annual funding approval
and may be terminated at their discretion. A reduction in spending by Federal
government agencies could limit the continued funding of our existing
contracts with them and could limit our ability to obtain additional
contracts.  These limitations, if significant, could have a material adverse
effect on our business.

     Additionally the failure of clients to pay significant amounts due us
for our services could adversely affect our business.  For example, we
received notification from a Federal government agency that we are entitled
to payments in excess of our billings.  However, the agency involved must
obtain specific funding approval for amounts owed to us and there can be no
assurance this funding approval will be obtained.

OUR CONTRACTS WITH GOVERNMENTAL AGENCIES ARE SUBJECT TO AUDIT, WHICH COULD
RESULT IN THE DISALLOWANCE OF CERTAIN COSTS

     Contracts with the Federal government and other governmental agencies
are subject to audit. Most of these audits are conducted by the Defense
Contract Audit Agency (DCAA), which reviews our overhead rates, operating
systems and cost proposals.  The DCAA may disallow costs if it determines
that we accounted for these costs incorrectly or in a manner inconsistent
with Cost Accounting Standards.  A disallowance of costs by the DCAA, or
other governmental auditors, could have a material adverse effect on our
business.

     In September 1995, we acquired PRC Environmental Management, Inc. (EMI).
 EMI also contracts with Federal government agencies and such contracts are
also subject to the same governmental audits.  At the time of acquisition,
audits had not yet been completed or finalized.  Accordingly, reserves were
established for potential disallowances.  Since then, the DCAA has completed
audits of EMI's contracts for the fiscal years 1987 through 1995.  As a
result of these audits and negotiations with the DCAA, the DCAA disallowed
approximately $4.4 million in costs which have been applied against the
established reserves.

OUR BUSINESS AND OPERATING RESULTS COULD BE ADVERSELY AFFECTED BY LOSSES
UNDER FIXED-PRICE CONTRACTS OR TERMINATION OF CONTRACTS AT THE CLIENT'S
DISCRETION

     We contract with Federal and state governments, as well as with the
commercial sector.  These contracts are often subject to termination at the
discretion of the client.  Additionally, we enter into various types of
contracts with our clients, including fixed-price contracts.  Fixed-price
contracts protect clients and expose us to a number of risks.  These risks
include underestimation of costs, problems with new technologies, unforeseen
costs or difficulties, delays beyond our control and economic and other
changes that may occur during the contract period.  Losses under fixed-price
contracts or termination of contracts at the discretion of the client could
have a material adverse effect on our business.

     In fiscal 1999, we had a contract change with Tele-Communications, Inc.
involving three turnkey contracts.  This change was due in part to
Tele-Communications, Inc.'s change in strategy from turnkey contracts to
direct service contracts in the upgrading of their network systems.

OUR INABILITY TO FIND QUALIFIED SUBCONTRACTORS COULD ADVERSELY AFFECT THE
QUALITY OF OUR SERVICE AND OUR ABILITY TO PERFORM UNDER CERTAIN CONTRACTS

     Under some of our contracts, we depend on the efforts and skills of
subcontractors for the performance of certain tasks.  Our reliance on
subcontractors varies from project to project.  In fiscal 1998 and the nine
months ended July 4, 1999, subcontractor costs comprised 22.3% and 23.1%,
respectively, of our gross revenue.  The


                                       5


absence of qualified subcontractors with whom we have a satisfactory
relationship could adversely affect the quality of our service and our
ability to perform under some of our contracts.

OUR INDUSTRY IS HIGHLY COMPETITIVE AND WE MAY BE UNABLE TO COMPETE EFFECTIVELY

     We provide specialized management consulting and technical services to a
broad range of public and private sector clients.  The market for our
services is highly competitive and we compete with many other firms.  These
firms range from small regional firms to large national firms which have
greater financial and marketing resources than ours.

     We focus primarily on the resource management, infrastructure and
communications business areas.  We provide services to our clients which
include Federal, state and local agencies, and organizations in the private
sector.

     We compete for projects and engagements with a number of competitors
which can vary from 10 to 100 firms. Historically, clients have chosen among
competing firms based on the quality and timeliness of the firm's service.
We believe, however, that price has become an increasingly important factor.

     We believe that our principal competitors include, in alphabetical
order, Black & Veatch LLP; Brown & Caldwell; Castle Tower Corporation; Camp,
Dresser & McKee; CH2M Hill Companies Ltd.; Dames & Moore Group; EA
Engineering, Science & Technology, Inc.; Earth Tech, Inc.; ICF Kaiser
International, Inc.; IT Group Inc.; Mastec, Inc.; Montgomery Watson; OSP
Consultants, Inc.; Roy F. Weston, Inc.; and URS Greiner Corporation.

OUR SERVICES EXPOSE US TO SIGNIFICANT RISKS OF LIABILITY AND OUR
INSURANCE POLICIES MAY NOT PROVIDE ADEQUATE COVERAGE

     Our services involve significant risks of professional and other
liabilities which may substantially exceed the fees we derive from our
services.  Our business activities could expose us to potential liability
under various environmental laws such as the Comprehensive Environmental
Response, Compensation and Liability Act of 1980 (CERCLA).  In addition, we
sometimes contractually assume liability under indemnification agreements.
We cannot predict the magnitude of such potential liabilities.

     We currently maintain comprehensive general liability, umbrella and
professional liability insurance policies. We believe that our insurance
policies are adequate for our business operations.  Professional liability
policies are "claims made" policies. Thus, only claims made during the term
of the policy are covered.  Should we terminate our professional liability
policies and not obtain retroactive coverage, we would be uninsured for
claims made after termination even if these claims are based on events or
acts that occurred during the term of the policy.  Additionally, our
insurance policies may not protect us against potential liability due to
various exclusions and retentions.  Should we expand into new markets, we may
not be able to obtain insurance coverage for such activities or, if insurance
is obtained, the dollar amount of any liabilities incurred could exceed our
insurance coverage.  Partially or completely uninsured claims, if successful
and of significant magnitude, could have a material adverse affect on our
business.

WE MAY BE PRECLUDED FROM PROVIDING CERTAIN SERVICES DUE TO CONFLICT OF
INTEREST ISSUES

     Many of our clients are concerned about potential or actual conflicts of
interest in retaining management consultants.  Federal government agencies
have formal policies against continuing or awarding contracts that would
create actual or potential conflicts of interest with other activities of a
contractor.  These policies, among other things, may prevent us from bidding
for or performing contracts resulting from or relating to certain work we
have performed for the government.  In addition, services performed for a
private client may create a conflict of interest that precludes or limits our
ability to obtain work from other public or private organizations.  We have,
on occasion, declined to bid on projects because of these conflicts of
interest issues.


                                       6



OUR INTERNATIONAL OPERATIONS EXPOSE US TO RISKS SUCH AS FOREIGN CURRENCY
FLUCTUATIONS

     In fiscal 1998 and the nine months ended July 4, 1999, approximately
3.2% and 3.8%, respectively, of our net revenue was derived from the
international marketplace.  Some contracts with our international clients are
denominated in foreign currencies.  As such, these contracts contain inherent
risks including foreign currency exchange risk and the risk associated with
expatriating funds from foreign countries. If our international revenue
increases, our exposure to foreign currency fluctuations will also increase.
We have entered into forward exchange contracts to address certain foreign
currency fluctuations.

WE COULD EXPERIENCE BUSINESS INTERRUPTIONS RELATING TO THE YEAR 2000

     We are working to resolve the potential impact of the year 2000 (Y2K) on
our business operations and the ability of our computerized information
systems to accurately process information that may be date-sensitive.  Any of
our programs that recognize a date using "00" as the year 1900 rather than
the (Y2K) could result in errors or system failures.

     We utilize a number of computer programs across our entire operation.
The primary information technology systems we utilize are the accounting and
financial and human resource information management systems.  We began our
risk assessment in 1995.  Since that time we have procured and implemented
certain accounting and financial reporting systems as well as contract
administration and billing systems that have been certified as Y2K compliant
by our vendors and have obtained assurances of Y2K compliance in all of our
acquired businesses.  In all cases, we believe that our financial and
accounting systems will be Y2K compliant in a timely manner and will not be
materially impacted by Y2K.

     We have extensive business with the Federal government.  Should the
Federal government, especially the DOD, experience significant business
interruptions relating to Y2K compliance, our business could be materially
impacted.  To the extent that other third parties upon which we rely, such as
banking institutions, clients and vendors, are unable to address their Y2K
issues in a timely manner, we could be materially impacted.  We believe that
the worst case scenario relating to the Y2K would be an extensive period of
time in which the Federal government and other third parties could not
process payments promptly, in addition to our financial institutions not
being able to supply us with our working capital needs.

     Additional risks associated with non-year 2000 compliance include:

     -  Our inability to invoice and process payments;

     -  Our inability to produce accurate and timely financials;

     -  The impact on our profitability; and

     -  Our potential liability to third parties for not meeting contracted
        deliverables.

                      SELLING STOCKHOLDERS

     On June 18, 1999, we acquired Utilities & C.C., Inc., a California
corporation ("UCCI"), through the merger of UCCI Acquisition Corporation, a
Delaware corporation and our wholly-owned subsidiary, into UCCI.  In
connection with this acquisition, we issued to the UCCI shareholders an
aggregate of 144,482 shares of our Common Stock (as adjusted to reflect a
post-closing purchase price adjustment).

     Under a Registration Rights Agreement dated as of June 18, 1999, we
agreed to register the shares of Common Stock and to use commercially
reasonable efforts to keep the registration statement effective until the
date on which all selling stockholders may sell their shares of Common Stock
under Rule 144 promulgated under the


                                       7



Securities Act of 1933, as amended (the "Securities Act"), without any volume
limitation.  Our registration of the shares of Common Stock does not
necessarily mean that the selling stockholders will sell all or any of the
shares.

     The shares listed below represent all of the shares that each selling
stockholder currently owns of our Common Stock.  Except as otherwise noted,
we know of no agreements among our stockholders which relate to voting or
investment power over our Common Stock.  Except as otherwise noted, the
address of each selling stockholder is c/o Utilities & C.C., Inc., 1555
Bedell Court, Roseville, California  95747.


                                             SHARES
                                          BENEFICIALLY          NUMBER OF
                                           OWNED PRIOR           SHARES
               NAMES                       TO OFFERING    %(1)   OFFERED
- ----------------------------------------- ------------    ----  ---------

Kenneth L. Shelton.......................     92,468        *     92,468
Lonny B. Cunningham......................     52,014        *     52,014

- --------------

*    Represents less than 1% of the outstanding shares of Common Stock.

     All selling stockholders are employees of UCCI, and no selling
stockholder has had any material relationship with us, or any of our
predecessors or affiliates, other than as an employee.  Because the selling
stockholders may sell all or part of their shares of Common Stock offered
hereby, no estimate can be given as to the number of shares of Common Stock
that will be held by any selling stockholder upon termination of any offering
made hereby.

                           PLAN OF DISTRIBUTION

     We are registering the shares of Common Stock on behalf of the selling
stockholders.  As used herein, "selling stockholders" includes donees and
pledgees selling shares received from a named selling shareholder after the
date of this Prospectus.  This Prospectus may also be used by transferees of
the selling stockholders or by other persons acquiring shares, including
brokers who borrow the shares to settle short sales of shares of Common
Stock.  We will bear all costs, expenses and fees in connection with the
registration of the shares offered hereby.  The selling stockholders will
bear brokerage commissions and any similar selling expenses associated with
the sale of shares.

     The selling stockholders may offer their shares of Common Stock at
various times in one or more of the following transactions:

     -  on the Nasdaq National Market;

     -  in the over-the-counter market;

     -  in transactions other than on the Nasdaq National Market or in the
        over-the-counter market;

     -  in connection with short sales of the shares of Common Stock;

     -  by pledge to secure debts and other obligations;


                                       8



     -  in connection with the writing of non-traded and exchange-traded call
        options, in hedge transactions and in settlement of other transactions
        in standardized or over-the-counter options; or

     -  in any combination of any of the above transactions.

     In connection with hedging transactions, broker-dealers or other
financial institutions may engage in short sales of the Common Stock in the
course of hedging the positions they assume with selling stockholders.  The
selling stockholders may also enter into options or other transactions with
broker-dealers or other financial institutions, which require the delivery to
such broker-dealer or other financial institution of the shares offered
hereby, which shares may be resold pursuant to this prospectus (as
supplemented or amended to reflect such transaction).

     The selling stockholders may sell their shares at market prices
prevailing at the time of sale, at prices related to such prevailing market
prices, at negotiated prices or at fixed prices.  The selling shareholders
may use broker-dealers to sell their shares.  If this happens, broker-dealers
will either receive discounts or commissions from purchasers of shares for
whom they acted as agents.

     The selling stockholders have advised us that they have not entered into
any agreements, understandings or arrangements with any underwriters or
broker-dealers regarding the sale of their securities, nor is there an
underwriter or coordinating broker acting in connection with the proposed
sale of shares by the selling stockholders.

     The selling stockholders and any broker-dealers that act in connection
with the sale of shares might be deemed to be "underwriters" within the
meaning of Section 2(11) of the Securities Act, and any commissions received
by such broker-dealers and any profit on the resale of the shares sold by
them while acting as principals might be deemed to be underwriting discounts
or commissions under the Securities Act.  We have agreed to indemnify each
selling stockholder against certain liabilities, including liabilities
arising under the Securities Act.  The selling stockholders may agree to
indemnify any agent, dealer or broker-dealer that participates in
transactions involving sales of the shares against certain liabilities,
including liabilities arising under the Securities Act.

     Because the selling stockholders may be deemed to be "underwriters"
within the meaning of Section 2(11) of the Securities Act, the selling
stockholders will be subject to the prospectus delivery requirements of the
Securities Act.  We have informed the selling stockholders that the
anti-manipulative provisions of Regulation M promulgated under the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), may apply to their
sales in the market.

     The selling stockholders also may resell all or a portion of the shares
in open market transactions in reliance upon Rule 144 under the Securities
Act, provided they meet the criteria and conform to the requirements of such
Rule.

     Upon being notified by a selling stockholder that any material
arrangement has been entered into with a broker-dealer for the sale of shares
through a block trade, special offering, exchange distribution or secondary
distribution or a purchase by a broker or dealer, we will file a supplement
to this Prospectus, if required, pursuant to Rule 424(b) under the Securities
Act, disclosing (i) the name of each such selling stockholder and of the
participating broker-dealer(s), (ii) the number of shares involved, (iii) the
price at which such shares were sold, (iv) the commissions paid or discounts
or concessions allowed to such broker-dealer(s), where applicable, and (v)
other facts material to the transaction.  In addition, upon being notified by
a selling stockholder that a donee or pledgee intends to sell more than 500
shares, we will file a supplement to this Prospectus.


                                       9



                     WHERE YOU CAN FIND MORE INFORMATION

     We file annual, quarterly and special reports, proxy statements and
other information with the Securities and Exchange Commission (SEC).  You may
read and copy any document we file at the SEC's public reference room at
450 Fifth Street, N.W., Washington, D.C. 20549.  Please call the SEC at
1-800-SEC-0330 for further information on the public reference room.  Our SEC
filings are also available to the public from the SEC's Website at "http:
//www.sec.gov."

     The SEC allows us to "incorporate by reference" the information we file
with them, which means that we can disclose important information to you by
referring you to those documents.  The information incorporated by reference
is considered to be part of this prospectus, and information that we file
later with the SEC will automatically update and supersede this information.
We incorporate by reference the documents listed below and any future filings
we will make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the
Exchange Act:

     1.  Annual Report on Form 10-K for the fiscal year ended October 4,
         1998, as filed with the SEC on December 31, 1998;

     2.  Annual Report on Form 10-K/A (Amendment No. 1) for the fiscal year
         ended October 4, 1998, as filed with the SEC on February 2, 1999;

     3.  Annual Report on Form 10-K/A (Amendment No. 2) for the fiscal year
         ended October 4, 1998, as filed with the SEC on March 5, 1999;

     4.  Quarterly Report on Form 10-Q for the fiscal quarter ended January
         3, 1999, as filed with the SEC on February 16, 1999;

     5.  Quarterly Report on Form 10-Q for the fiscal quarter ended April 4,
         1999, as filed with the SEC on May 19, 1999;

     6.  Quarterly Report on Form 10-Q for the fiscal quarter ended July 4,
         1999, as filed with the SEC on August 18, 1999;

     7.  Current Report on Form 8-K for the event of September 22, 1998, as
         filed with the SEC on October 7, 1998;

     8.  Current Report on Form 8-K/A for event of September 22, 1998, as
         filed with the SEC on December 1, 1998;

     9.  Definitive Proxy Statement, as filed with the SEC on December 31,
         1998, for the 1999 Annual Meeting of Stockholders;

     10. Definitive Proxy Statement (Amendment No. 1), as filed with the SEC
         on January 12, 1999, for the 1999 Annual Meeting of Stockholders; and

     11. The description of the Common Stock set forth in the Registration
         Statement on Form 8-A dated November 13, 1991, including any
         amendments or reports filed for the purpose of updating such
         description.

     You may request a copy of these filings, at no cost, by writing or
telephoning James M. Jaska as follows:


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                          Tetra Tech, Inc.
                          Attention:  Investor Relations
                          670 North Rosemead Boulevard
                          Pasadena, California 91107
                          (626) 351-4664

     This prospectus is part of a registration statement we filed with the
SEC. You should rely only on the information or representations provided in
this prospectus.  We have authorized no one to provide you with different
information. We are not making an offer of these securities in any state
where the offer is not permitted.  You should not assume that the information
in this prospectus is accurate as of any date other than the date on the
front of the document.

                                  LEGAL MATTERS

     The validity of the Common Stock offered hereby will be passed on for us
by Riordan & McKinzie, a Professional Corporation, Los Angeles, California.
Certain principals of Riordan & McKinzie own, in the aggregate, approximately
160,000 shares of Common Stock.

                                    EXPERTS

     The financial statements and the related financial statement schedule
incorporated in this prospectus by reference from our Annual Report on
Form 10-K for the year ended October 4, 1998 have been audited by Deloitte &
Touche LLP, independent auditors, as stated in their reports, which are
incorporated herein by reference, and have been so incorporated in reliance
upon the reports of such firm given upon their authority as experts in
accounting and auditing.


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