<SEC-DOCUMENT>0000831641-20-000144.txt : 20201120
<SEC-HEADER>0000831641-20-000144.hdr.sgml : 20201120
<ACCEPTANCE-DATETIME>20201120190442
ACCESSION NUMBER:		0000831641-20-000144
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20201118
FILED AS OF DATE:		20201120
DATE AS OF CHANGE:		20201120

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BROWNLIE WILLIAM R
		CENTRAL INDEX KEY:			0001346227

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19655
		FILM NUMBER:		201333855

	MAIL ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TETRA TECH INC
		CENTRAL INDEX KEY:			0000831641
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-ENGINEERING SERVICES [8711]
		IRS NUMBER:				954148514
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0927

	BUSINESS ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107
		BUSINESS PHONE:		6263514664

	MAIL ADDRESS:	
		STREET 1:		3475 EAST FOOTHILL BOULEVARD
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91107
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_160591706498164.xml
<DESCRIPTION>FORM 4
<TEXT>
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    <periodOfReport>2020-11-18</periodOfReport>

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    <issuer>
        <issuerCik>0000831641</issuerCik>
        <issuerName>TETRA TECH INC</issuerName>
        <issuerTradingSymbol>TTEK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001346227</rptOwnerCik>
            <rptOwnerName>BROWNLIE WILLIAM R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3475 EAST FOOTHILL BOULEVARD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PASADENA,</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91107</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Chief Engineer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
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                <footnoteId id="F5"/>
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                <value>2022-11-18</value>
            </expirationDate>
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                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
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                </transactionShares>
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    <footnotes>
        <footnote id="F1">Shares automatically acquired upon the vesting of restricted stock units (RSUs).</footnote>
        <footnote id="F2">82 of the RSUs vested on 11/18/2020 are subject to the Reporting Person's deferral into the Issuer's Deferred Compensation Plan, and will be settled in shares of the Issuer's common stock according to the Reporting Person's elected distribution schedule.</footnote>
        <footnote id="F3">Shares acquired pursuant to vesting of performance stock units (PSUs) earned under 2015 Equity Incentive Plan.</footnote>
        <footnote id="F4">Represents the combined number of shares withheld to pay the related tax liability on a total of 6,878 performance stock units (PSUs) and 1,782 restricted stock units (RSUs) which were vested and released on 11/18/2020.</footnote>
        <footnote id="F5">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.</footnote>
        <footnote id="F6">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.</footnote>
        <footnote id="F7">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.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Preston Hopson, Attorney-in-fact for William R. Brownlie</signatureName>
        <signatureDate>2020-11-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
