<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-02-08</periodOfReport>

    <issuer>
        <issuerCik>0000098222</issuerCik>
        <issuerName>TIDEWATER INC</issuerName>
        <issuerTradingSymbol>TDW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001057586</rptOwnerCik>
            <rptOwnerName>MURRILL PAUL W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TIDEWATER INC.</rptOwnerStreet1>
            <rptOwnerStreet2>601 POYDRAS ST., SUITE 19000</rptOwnerStreet2>
            <rptOwnerCity>NEW ORLEANS</rptOwnerCity>
            <rptOwnerState>LA</rptOwnerState>
            <rptOwnerZipCode>70130</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-02-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>I</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5268.8</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.93</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5268.8</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Transferred to alternative investment pursuant to election made in accordance with Tidewater Inc. Deferred Compensation Plan for Outside Directors.</footnote>
        <footnote id="F2">The security converts to common stock on a one-for-one basis.</footnote>
        <footnote id="F3">Phantom Stock Units are paid in cash upon termination of Board service or such other date chosen by reporting person in accordance with Tidewater Deferred Compensation Plan For Outside Directors.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Paul w. Murrill, By: Michael L. Goldblatt, Agent and Attorney-in-Fact</signatureName>
        <signatureDate>2006-02-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-02-08
0000098222
TIDEWATER INC
TDW
0001057586
MURRILL PAUL W
C/O TIDEWATER INC.
601 POYDRAS ST., SUITE 19000
NEW ORLEANS
LA
70130
1
0
0
0
Phantom Stock Units
0
2006-02-08
4
I
0
5268.8
55.93
D
Common Stock
5268.8
0
D
Transferred to alternative investment pursuant to election made in accordance with Tidewater Inc. Deferred Compensation Plan for Outside Directors.
The security converts to common stock on a one-for-one basis.
Phantom Stock Units are paid in cash upon termination of Board service or such other date chosen by reporting person in accordance with Tidewater Deferred Compensation Plan For Outside Directors.
Paul w. Murrill, By: Michael L. Goldblatt, Agent and Attorney-in-Fact
2006-02-09