Exhibit 23 INDEPENDENT AUDITORS' CONSENT We consent to the incorporation by reference in Registration Statement Nos. 33-46240, 33-47533, 33-80606, and 33-94706 on Form S-8 of Tetra Tech, Inc. of our report dated March 13, 1998 appearing in this Form 8-K/A of Tetra Tech, Inc. DELOITTE & TOUCHE LLP Los Angeles, California March 13, 1998