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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   ----------

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934

                               (Amendment No. 1)*

                                   ----------

                                Tetra Tech, Inc.
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                                (Name of Issuer)

                                  Common Stock
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                         (Title of Class of Securities)

                                    88162G103
                             ----------------------
                                 (CUSIP Number)


                                December 31, 2003
              -----------------------------------------------------
             (Date of Event Which Requires Filing of this Statement)


     Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:

                                [X]  Rule 13d-1(b)
                                [_]  Rule 13d-1(c)
                                [_]  Rule 13d-1(d)

                                   ----------

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

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                               Page 1 of 9 pages



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CUSIP No. 88162G103                    13G                     Page 2 of 9 Pages
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1    NAME OF REPORTING PERSON
     S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

          Columbia Wanger Asset Management, L.P. 36-3820584

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2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

          Not Applicable                                            (a) [_]
                                                                    (b) [_]

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3    SEC USE ONLY

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4    CITIZENSHIP OR PLACE OF ORGANIZATION

          Delaware

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                     5    SOLE VOTING POWER
NUMBER OF SHARES
                               None
BENEFICIALLY
                     -----------------------------------------------------------
OWNED BY             6    SHARED VOTING POWER

EACH                           2,711,000

REPORTING            -----------------------------------------------------------
                     7    SOLE DISPOSITIVE POWER
PERSON WITH
                               None

                     -----------------------------------------------------------
                     8    SHARED DISPOSITIVE POWER

                               2,711,000

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9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          2,711,000

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10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

          Not Applicable                                                [_]

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11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

          4.987%

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12   TYPE OF REPORTING PERSON

          IA

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-------------------                                            -----------------
CUSIP No. 88162G103                    13G                     Page 3 of 9 Pages
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1    NAME OF REPORTING PERSON
     S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

          WAM Acquisition GP, Inc.

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2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

          Not Applicable                                            (a) [_]
                                                                    (b) [_]
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3    SEC USE ONLY

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4    CITIZENSHIP OR PLACE OF ORGANIZATION

          Delaware

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 NUMBER OF SHARES     5    SOLE VOTING POWER

 BENEFICIALLY                   None

 OWNED BY             ----------------------------------------------------------
                      6    SHARED VOTING POWER
 EACH
                                2,711,000
 REPORTING
                      ----------------------------------------------------------
 PERSON WITH          7    SOLE DISPOSITIVE POWER

                                None

                      ----------------------------------------------------------
                      8    SHARED DISPOSITIVE POWER

                                2,711,000
--------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          2,711,000

--------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

          Not Applicable                                                [_]

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11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

          4.987%

--------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON

          CO

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Item 1(a)  Name of Issuer:

                 Tetra Tech, Inc.

Item 1(b)  Address of Issuer's Principal Executive Offices:

                 3475 East Foothill Boulevard
                 Pasadena, California  91107

Item 2(a)  Name of Person Filing:

                 Columbia Wanger Asset Management, L.P. ("WAM")
                 WAM Acquisition GP, Inc., the general partner of WAM ("WAM GP")

Item 2(b)  Address of Principal Business Office:

                 WAM and WAM GP are both located at:

                 227 West Monroe Street, Suite 3000
                 Chicago, Illinois  60606

Item 2(c)  Citizenship:

                 WAM is a Delaware limited partnership; and WAM GP is a
                 Delaware corporation

Item 2(d)  Title of Class of Securities:

                 Common Stock

Item 2(e)  CUSIP Number:

                 88162G103

Item 3     Type of Person:

                 (e)  WAM is an Investment Adviser registered under section
                      203 of the Investment Advisers Act of 1940; WAM GP is
                      the General Partner of the Investment Adviser.

                               Page 4 of 9 pages



Item 4     Ownership (at December 31, 2003):

                 (a)  Amount owned "beneficially" within the meaning of rule
                      13d-3:

                      2,711,000

                 (b)  Percent of class:

                      4.987% (based on 54,365,956 shares outstanding as of
                      December 8, 2003).

                 (c)  Number of shares as to which such person has:

                             (i) sole power to vote or to direct the vote:  none
                            (ii) shared power to vote or to direct the vote:
                                 2,711,000
                           (iii) sole power to dispose or to direct the
                                 disposition of:  none
                            (iv) shared power to dispose or to direct
                                 disposition of:  2,711,000

Item 5     Ownership of Five Percent or Less of a Class:

                 If this statement is being filed to report the fact that as of
                 the date hereof the reporting person has ceased to be the
                 beneficial owner of more than five percent of the class of
                 securities, check the following: [X]

Item 6     Ownership of More than Five Percent on Behalf of Another Person:

                 Not Applicable

Item 7     Identification and Classification of the Subsidiary Which Acquired
           the Security Being Reported on by the Parent Holding Company:

                 Not Applicable

Item 8     Identification and Classification of Members of the Group:

                 Not Applicable

Item 9     Notice of Dissolution of Group:

                 Not Applicable

                               Page 5 of 9 Pages



Item 10    Certification:

                 By signing below I certify that, to the best of my knowledge
           and belief, the securities referred to above were acquired and are
           held in the ordinary course of business and were not acquired and are
           not held for the purpose of or with the effect of changing or
           influencing the control of the issuer of the securities and were not
           acquired and are not held in connection with or as a participant in
           any transaction having that purpose or effect.


                               Page 6 of 9 Pages



                                    Signature
                                    ---------

     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.


Date: February 10, 2004


                 The undersigned corporation, on the date above written, agrees
                 and consents to the joint filing on its behalf of this Schedule
                 13G in connection with its beneficial ownership of the security
                 reported herein.


                                        WAM Acquisition GP, Inc.
                                         for itself and as general partner of
                                         COLUMBIA WANGER ASSET MANAGEMENT, L.P.


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                                Bruce H. Lauer
                                                Senior Vice President and
                                                Secretary


                               Page 7 of 9 Pages



                                  Exhibit Index
                                  -------------

Exhibit 1        Joint Filing Agreement dated as of February 10, 2004 by and
                 among Columbia Wanger Asset Management, L.P. and WAM
                 Acquisition GP, Inc.


                               Page 8 of 9 Pages



                                                                       EXHIBIT 1

                             JOINT FILING AGREEMENT

     The undersigned hereby agree to the joint filing of the Schedule 13G to
which this Agreement is attached.


                 Dated: February 10, 2004


                                        WAM Acquisition GP, Inc.
                                         for itself and as general partner of
                                         COLUMBIA WANGER ASSET MANAGEMENT, L.P.


                                        By: /s/ Bruce H. Lauer
                                            ------------------------------------
                                                Bruce H. Lauer
                                                Senior Vice President and
                                                Secretary


                               Page 9 of 9 pages