EXHIBIT 99.1

                                                                    July 2, 2001


                  TETRA TECH UPDATES GUIDANCE FOR THIRD QUARTER
                        BASED ON CHARGE FOR METRICOM WORK

PASADENA, CALIFORNIA. Tetra Tech, Inc. (NASDAQ: TTEK) announced today that it
will update its guidance for the third quarter, based on the decision by
Metricom, Inc. (NASDAQ: MCOM) to file for protection under Chapter 11 of the
U.S. Bankruptcy Code, and to engage in restructuring discussions with its
creditors. Since September 1999, Tetra Tech has performed wireless network
development work under several contracts in connection with Metricom's Ricochet
network. Tetra Tech has notified Metricom that it is terminating those
contracts. Although Tetra Tech has received payments from Metricom through May
of this year, Tetra Tech has outstanding accounts receivable with Metricom in
the aggregate amount of $38.3 million. Tetra Tech will take a charge in the
third quarter to provide for this doubtful account.

In the third quarter, Tetra Tech also anticipate a lower effective income tax
rate, down from 42% down to 39%, and a retroactive tax credit. Because of the
charge for Metricom's doubtful account and the anticipated reduction of our tax
rate, the Company estimates that it will report a loss of approximately 11 cents
per share for the third quarter, assuming no recovery from the bankruptcy
process. Should Tetra Tech recover proceeds from the bankruptcy process, it will
be reported during the quarter in which it is received.

The exact amount of the charge net of any estimated recovery has not yet been
determined, however, it will be reflected in Tetra Tech's results for the third
quarter ended July 1, 2001. Tetra Tech will issue an earnings release on or
about July 18, 2001 which will provide additional guidance as to the amount of
the charge and its effect on earnings per share.

Excluding the charge and tax credit, Tetra Tech remains confident about meeting
the guidance provided earlier for the third quarter and fiscal year. According
to Li-San Hwang, Chairman and Chief Executive Officer, "our overall business
continues to be strong, especially in water-related projects, in-building
communications projects and energy related projects. Demand for solutions to
complex problems continues to drive our growth and diversity. The strong
national demand for energy infrastructure is continuing to have a positive
impact on all three of our business areas, and we anticipate that this impact
will continue."

Metricom is a provider of high-speed wireless data services. In addition,
Metricom provides wireless modems and software to allow access to network
applications.

Investors will have the opportunity to listen to a conference call over the
Internet discussing this event. The live call and replay will occur on Investor
Broadcast Networks, Vcall Web site, located at http://www.vcall.com on Tuesday,
July 3, 2001 at 8:00 a.m. PDT. ABOUT TETRA TECH (www.tetratech.com)




Tetra Tech is a leading provider of specialized management consulting and
technical services in three principal business areas: resource management,
infrastructure and communications. The Company's clients include a diverse base
of public and private sector organizations serviced through more than 150
offices located in the United States and internationally.

CONTACT: Li-San Hwang, President and CEO, or Mike Bieber, Investor Relations
626/351-4664

THIS NEWS RELEASE CONTAINS VARIOUS "FORWARD-LOOKING STATEMENTS" WITHIN THE
MEANING OF THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995. THESE INCLUDE
STATEMENTS CONCERNING TETRA TECH'S 2001 FINANCIAL AND BUSINESS PROSPECTS. THE
STATEMENTS, WHICH REPRESENT TETRA TECH'S EXPECTATIONS OR BELIEFS CONCERNING
VARIOUS FUTURE EVENTS, ARE BASED ON CURRENT EXPECTATIONS THAT INVOLVE A NUMBER
OF RISKS AND UNCERTAINTIES THAT COULD CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY
FROM THOSE OF SUCH FORWARD-LOOKING STATEMENTS. THESE INCLUDE RISKS ASSOCIATED
WITH ITS ACQUISITION STRATEGY; FLUCTUATIONS IN ITS QUARTERLY OPERATING RESULTS
AND STOCK PRICE; MANAGEMENT OF ITS GROWTH STRATEGY; LOSS OF KEY PERSONNEL OR ITS
INABILITY TO ATTRACT AND RETAIN QUALIFIED PERSONNEL; CHANGES IN EXISTING LAWS
AND REGULATIONS; CONCENTRATION OF REVENUES FROM AGENCIES OF THE FEDERAL
GOVERNMENT AND REDUCTIONS IN SPENDING BY THESE AGENCIES; AUDIT OF ITS CONTRACTS
WITH GOVERNMENTAL AGENCIES; LOSSES UNDER FIXED-PRICE CONTRACTS OR TERMINATION OF
CONTRACTS AT THE CLIENT'S DISCRETION; INABILITY TO FIND QUALIFIED
SUBCONTRACTORS; COMPETITION IN ITS INDUSTRY; RISKS OF PROFESSIONAL AND OTHER
LIABILITIES; CONFLICT OF INTEREST ISSUES; FOREIGN CURRENCY FLUCTUATIONS; AND
OTHER UNCERTAINTIES OR RISKS REPORTED FROM TIME TO TIME IN TETRA TECH'S REPORTS
TO THE SECURITIES AND EXCHANGE COMMISSION, INCLUDING THOSE UNDER THE HEADING
"RISK FACTORS" IN ITS FORM 10-K FOR THE FISCAL YEAR ENDED OCTOBER 1, 2000. TETRA
TECH UNDERTAKES NO DUTY TO UPDATE THE FORWARD-LOOKING STATEMENTS.