FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
1. Name and Address of Reporting Person * Amidon Derek G 2. Issuer Name and Ticker or Trading Symbol TETRA TECH INC [ TTEK ] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable)_____ Director                    _____ 10% Owner
__X__ Officer (give title below)    _____ Other (specify below)
SVP, Comm./Int'l Svcs. Group
(Last)         (First)         (Middle)
3475 EAST FOOTHILL BOULEVARD
3. Date of Earliest Transaction (MM/DD/YYYY)
11/18/2020
(Street)
PASADENA, CA 91107
(City)       (State)       (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)
 
6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
COMMON STOCK  11/18/2020    M    539  A $0 (1) 4895  D   
COMMON STOCK  11/18/2020    M    524  A $0 (1) 5419  D   
COMMON STOCK  11/18/2020    A    6878  A $0 (2) 12297  D   
COMMON STOCK  11/18/2020    F    4819  D $122 (3) 7478  D   

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
RESTRICTED STOCK UNITS (RIGHT TO RECEIVE)  $0.0  11/18/2020    M        539   11/18/2019 (4) 11/18/2022  COMMON STOCK  539.0  $0  1078  D   
RESTRICTED STOCK UNITS (RIGHT TO RECEIVE)  $0.0  11/18/2020    M        524   11/18/2020 (5) 11/21/2023  COMMON STOCK  524.0  $0  1570  D   
RESTRICTED STOCK UNITS (RIGHT TO RECEIVE)  $0.0  11/19/2020    A     2295      11/18/2021 (6) 11/19/2024  COMMON STOCK  2295.0  $0  2295  D   

Explanation of Responses:
(1)  Shares automatically acquired upon the vesting of restricted stock units (RSUs).
(2)  Shares acquired pursuant to vesting of performance stock units (PSUs) earned under 2015 Equity Incentive Plan.
(3)  Represents the combined number of shares withheld to pay the related tax liability on a total of 6,878 performance stock units (PSUs) and 1,771 restricted stock units (RSUs) which vested on 11/18/2020.
(4)  The restricted stock units (RSUs) become vested as to 25% of the shares underlying the RSUs on November 18, 2019, and on each of anniversary of that date until the RSUs are fully vested.
(5)  The RSUs become vested as to 25% of the shares on November 18, 2020, and the anniversary of that date going forward until fully vested.
(6)  The RSUs become vested as to 25% of the shares on November 18, 2021, and the anniversary of that date going forward until fully vested.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Amidon Derek G
3475 EAST FOOTHILL BOULEVARD
PASADENA, CA 91107


SVP, Comm./Int'l Svcs. Group

Signatures
/s/ Preston Hopson, Attorney-in-fact for Derek G. Amidon 11/20/2020
**Signature of Reporting Person Date