Exhibit 99.1

August 11, 2006

Tetra Tech to Seek Five-Day Extension for Filing 10-Q

Pasadena, California. Tetra Tech, Inc. (NASDAQ: TTEK) announced today that it intends to submit a Rule 12b-25 filing related to its Quarterly Report on Form 10-Q for the fiscal quarter ended July 2, 2006. The Company is in the process of voluntarily reviewing its historical stock option grant practices.

The Company has completed its review of stock options granted in fiscal years 2006, 2005 and 2004, and has preliminarily determined there is no material impact on its financial statements from options granted during those periods. The Company is now reviewing stock options granted in prior periods. The review to date indicates no intentional misstatements. The Company currently believes that it will complete its review in the next few days and anticipates filing its Quarterly Report by August 16, 2006 as permitted by Rule 12b-25.

About Tetra Tech (www.tetratech.com)

Tetra Tech is a leading provider of consulting, engineering and technical services. With approximately 7,500 associates located in the United States and internationally, the Company supports commercial and government clients in the areas of resource management and infrastructure. Tetra Tech’s services include research and development, applied science and technology, engineering design, program management, construction management, and operations and maintenance.

CONTACT: Mike Bieber, (626) 351-4664

Forward-Looking Statements

This news release contains forward-looking statements that are subject to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include information concerning future events and the future financial performance of Tetra Tech that involve risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. Readers are urged to read the documents filed by Tetra Tech with the SEC, specifically the most recent reports on Form 10-K, 10-Q, and 8-K, each as it may be amended from time to time, which identify risk factors that could cause actual results to differ materially from the forward-looking statements. Among the important factors or risks that could cause actual results or events to differ materially from those in the forward-looking statements in this release are: fluctuations in quarterly operating results; the impact of downturns in the financial markets and reductions in government budgets; volatility of common stock value; concentration of revenues from government agencies and funding disruptions by these agencies; failure to properly manage projects; acquisition strategy risks; management of growth strategy; use of the percentage-of-completion method of accounting; adverse resolution of an IRS examination; loss of key personnel or the inability to attract and retain qualified personnel; implementation of the enterprise resource planning system; international operations risks; credit risks associated with commercial clients; violations of government contractor regulations; competitive bidding for government contracts; the affect of a negative government audit; the inability to accurately estimate contract risks, revenue, and costs; backlog cancellation and adjustments; client base consolidation; failure of partners to perform on joint projects; inability to find qualified subcontractors; changes in existing environmental laws, regulations, or programs; competition; restrictive covenants in debt agreements; risks of professional and other liabilities; adverse resolution of litigation; conflict of interest issues; changes in accounting for equity-related compensation; expenses associated with corporate governance; and disruption of operations due to computer viruses or terrorism. Any projections in this release

are based on limited information currently available to Tetra Tech, which is subject to change. Although any such projections and the factors influencing them will likely change, Tetra Tech will not necessarily update the information, since Tetra Tech will only provide guidance at certain points during the year. Readers should not place undue reliance on forward-looking statements since such information speaks only as of the date of this release.