Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated December 27, 2006 relating to the financial statements, management’s assessment of the effectiveness of internal control over financial reporting and the effectiveness of internal control over financial reporting, which appears in the 2006 Annual Report to Shareholders, which is incorporated by reference in Tetra Tech, Inc.’s Annual Report on Form 10-K for the year ended October 1, 2006.  We also consent to the incorporation by reference of our report dated December 27, 2006 relating to the financial statement schedule, which appears in such Annual Report on Form 10-K.

/s/ PRICEWATERHOUSECOOPERS LLP

Los Angeles, California

August 2, 2007