Statement of Changes in Beneficial Ownership (4)

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 * O'Rourke Brendan M.	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, Enterprise Risk Mgmt.
(Last)          (First)          (Middle) 3475 EAST FOOTHILL BLVD.	3. Date of Earliest Transaction (MM/DD/YYYY) 1/29/2021
(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	1/29/2021		M		250	A	$0 (1)	1708 (2)	D
COMMON STOCK	1/29/2021		F		94 (3)	D	$121.57 (4)	1614	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	1/29/2021		M			250	1/29/2019 (5)	1/29/2022	COMMON STOCK	250.0	$0	250	D

Explanation of Responses:
(1)	Shares were automatically acquired upon the vesting of restricted stock units (RSUs).
(2)	Amount of securities beneficially owned was updated to reflect that 58 shares of common stock were acquired by the Reporting Person on December 15, 2020, pursuant to the Tetra Tech, Inc. Employee Stock Purchase Plan (ESPP).
(3)	Represents the number of shares withheld to pay the related tax liability on the restricted stock units (RSUs) which vested on 01/29/2021.
(4)	The closing trading price of the underlying common stock on 01/29/2021 when the RSUs vested.
(5)	The RSUs became vested as to 25% of the shares on January 29, 2019, and the anniversary of that date going forward until fully vested.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
O'Rourke Brendan M. 3475 EAST FOOTHILL BLVD. PASADENA, CA 91107			SVP, Enterprise Risk Mgmt.

Signatures
/s/ Preston Hopson, Attorney-in-fact for Brendan O'Rourke		2/1/2021
**Signature of Reporting Person		Date