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.
                             (Name of Issuer)

                               Common Stock
                      (Title of Class of Securities)

                                88162G103
                              (CUSIP Number)

                            December 29, 2006
         (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).



















CUSIP: 88162G103                                                Page 1 of 7




 1   NAMES OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
     Capital Research and Management Company
     95-1411037

 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE
     INSTRUCTIONS)                                                 (a)

                                                                    (b)
 3   SEC USE ONLY


 4   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware

             5   SOLE VOTING POWER

                  315,400


             6   SHARED VOTING POWER
 NUMBER OF
   SHARES         NONE
BENEFICIALL
 Y OWNED BY
             7   SOLE DISPOSITIVE POWER
    EACH
 REPORTING        315,400
   PERSON
   WITH:
             8   SHARED DISPOSITIVE POWER

                  NONE

 9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     315,400     Beneficial ownership disclaimed pursuant to Rule 13d-4



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


 11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     0.5%

 12  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

     IA







CUSIP: 88162G103                                                Page 2 of 7







 1   NAMES OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
     SMALLCAP World Fund, Inc.
     95-4253845

 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE
     INSTRUCTIONS)                                                 (a)

                                                                    (b)
 3   SEC USE ONLY


 4   CITIZENSHIP OR PLACE OF ORGANIZATION

     Maryland

             5   SOLE VOTING POWER

                  NONE


             6   SHARED VOTING POWER
 NUMBER OF
   SHARES         NONE
BENEFICIALL
 Y OWNED BY
             7   SOLE DISPOSITIVE POWER
    EACH
 REPORTING        NONE
   PERSON
   WITH:
             8   SHARED DISPOSITIVE POWER

                  NONE

 9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     240,500



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


 11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     0.4%

 12  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

     IV






CUSIP: 88162G103                                                Page 3 of 7






                  SECURITIES AND EXCHANGE COMMISSION
                         Washington, DC 20549

                             Schedule 13G
               Under the Securities Exchange Act of 1934


Amendment No. 1

Item 1(a)     Name of Issuer:
       Tetra Tech Inc.

Item 1(b)     Address of Issuer's Principal Executive Offices:
       3475 East Foothill Blvd
       Pasadena CA 91107

Item 2(a)     Name of Person(s) Filing:
       Capital Research and Management Company and SMALLCAP World
       Fund, Inc.

Item 2(b)     Address of Principal Business Office or, if none,
       Residence:
       333 South Hope Street
       Los Angeles, CA  90071

Item 2(c)     Citizenship:   N/A

Item 2(d)     Title of Class of Securities:
       Common Stock

Item 2(e)     CUSIP Number:
       88162G103

Item 3     If this statement is filed pursuant to sections 240.13d-1(b)
       or 240.13d-2(b) or (c), check whether the person filing is a:
       (d)     [X]     Investment company registered under section 8
            of the Investment Company Act of 1940 (15 U.S.C. 80a-8).
       (e)      [X]     An investment adviser in accordance with
            section 240.13d-1(b)(1)(ii)(E).

Item 4     Ownership

       Provide the following information regarding the aggregate
       number and percentage of the class of securities of the issuer
       identified in Item 1.

       See pages 2 and 3

       (a)    Amount beneficially owned:
       (b)    Percent of class:
       (c)    Number of shares as to which the person has:
       (i)    Sole power to vote or to direct the vote:
       (ii)   Shared power to vote or to direct the vote:
       (iii)  Sole power to dispose or to direct the disposition of:
       (iv)   Shared power to dispose or to direct the disposition of:



CUSIP: 88162G103                                                Page 4 of 7







       Capital Research and Management Company, an investment adviser
       registered under Section 203 of the Investment Advisers Act of
       1940 is deemed to be the beneficial owner of 315,400 shares or
       0.5% of the 57,732,712 shares of Common Stock believed to be
       outstanding as a result of acting as investment adviser to
       various investment companies registered under Section 8 of the
       Investment Company Act of 1940.

       SMALLCAP World Fund, Inc., an investment company registered
       under the Investment Company Act of 1940, which is advised by
       Capital Research and Management Company, is the beneficial
       owner of 240,500 shares or 0.4% of the 57,732,712 shares of
       Common Stock believed to be outstanding.

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: N/A

Item 7     Identification and Classification of the Subsidiary Which
       Acquired the Security Being Reported on By the Parent Holding
       Company or Control Person.: N/A

Item 8     Identification and Classification of Members of the Group:
       N/A

Item 9     Notice of Dissolution of Group:  N/A

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.

     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 7, 2007

        Signature:     *Paul G. Haaga, Jr.
        Name/Title:    Paul G. Haaga, Jr., Executive Vice
                       President
                       Capital Research and Management Company


CUSIP: 88162G103                                                Page 5 of 7





        Date:          February 7, 2007

        Signature:     *Chad L. Norton
        Name/Title:    Chad L. Norton, Secretary
                       SMALLCAP World Fund, Inc.



        *By    /s/ Liliane Corzo
               Liliane Corzo
               Attorney-in-fact

          Signed pursuant to a Power of Attorney dated November 14,
          2006 included as an Exhibit to Schedule 13F filed with the
          Securities and Exchange Commission by Capital Research and
          Management Company on November 14, 2006.










































CUSIP: 88162G103                                                Page 6 of 7




                               AGREEMENT

                            Los Angeles, CA
                           February 7, 2007

  Capital Research and Management Company ("CRMC") and SMALLCAP World
Fund, Inc. ("SCWF") hereby agree to file a joint statement on Schedule
13G under the Securities Exchange Act of 1934 (the "Act") in connection
with their beneficial ownership of Common Stock issued by Tetra Tech
Inc.

  CRMC and SCWF state that they are each entitled to individually use
Schedule 13G pursuant to Rule 13d-1(c) of the Act.

  CRMC and SCWF are each responsible for the timely filing of the
statement and any amendments thereto, and for the completeness and
accuracy of the information concerning each of them contained therein
but are not responsible for the completeness or accuracy of the
information concerning the others.



                 CAPITAL RESEARCH AND MANAGEMENT COMPANY

                 BY:              *Paul G. Haaga, Jr.
                                  Paul G. Haaga, Jr., Executive
                                   Vice President
                                   Capital Research and Management
                                   Company


                 SMALLCAP WORLD FUND, INC.

                 BY:              *Chad L. Norton
                                  Chad L. Norton, Secretary
                                   SMALLCAP World Fund, Inc.


*By  /s/ Liliane Corzo
     Liliane Corzo
     Attorney-in-fact

     Signed pursuant to a Power of Attorney dated November 14, 2006
     included as an Exhibit to Schedule 13F filed with the Securities
     and Exchange Commission by Capital Research and Management Company
     on November 14, 2006.















CUSIP: 88162G103                                                Page 7 of 7