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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-30</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197244</rptOwnerCik>
            <rptOwnerName>DICK STEPHEN W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TIDEWATER INC.</rptOwnerStreet1>
            <rptOwnerStreet2>601 POYDRAS ST., SUITE 1900</rptOwnerStreet2>
            <rptOwnerCity>NEW ORLEANS</rptOwnerCity>
            <rptOwnerState>LA</rptOwnerState>
            <rptOwnerZipCode>70130</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>31727</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2748</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trustee</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>37.55</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>6000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-03-30</value>
            </exerciseDate>
            <expirationDate>
                <value>2015-03-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock award under the Tidewater Inc. 1997 Stock Incentive Plan. The Plan pursuant to which the restricted stock award was granted provides for tax withholding rights. The restricted stock award vests at the rate of 25% per year if Return on Total Capital (ROTC) for the year of determination exceeds the greater of 15% or the average of the prior four year's ROTC.  Any unvested restricted stock will automatically vest on March 30, 2009.</footnote>
        <footnote id="F2">Acquired on a periodic basis by the Trustee of the Tidewater Inc. 401(k) Savings Plan. Includes shares acquired for my account through March 31, 2005.</footnote>
        <footnote id="F3">Stock option granted under the Tidewater Inc. 2001 Stock Incentive Plan in transaction exempt under Rule 16b-3. The Plan pursuant to which the reported option was granted provides for tax withholding rights. The option vests on March 30, 2005.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Stephen Dick, by: Michael Goldblatt, Agent and Attorney-in-Fact</signatureName>
        <signatureDate>2005-04-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-03-30
0000098222
TIDEWATER INC
TDW
0001197244
DICK STEPHEN W
C/O TIDEWATER INC.
601 POYDRAS ST., SUITE 1900
NEW ORLEANS
LA
70130
0
1
0
0
Executive Vice President
Common Stock
2005-03-30
4
A
0
8000
A
31727
D
Common Stock
2748
I
By Trustee
Stock Option (Right to Buy)
37.55
2005-03-30
4
A
0
6000
A
2005-03-30
2015-03-30
Common Stock
6000
6000
D
Restricted stock award under the Tidewater Inc. 1997 Stock Incentive Plan. The Plan pursuant to which the restricted stock award was granted provides for tax withholding rights. The restricted stock award vests at the rate of 25% per year if Return on Total Capital (ROTC) for the year of determination exceeds the greater of 15% or the average of the prior four year's ROTC.  Any unvested restricted stock will automatically vest on March 30, 2009.
Acquired on a periodic basis by the Trustee of the Tidewater Inc. 401(k) Savings Plan. Includes shares acquired for my account through March 31, 2005.
Stock option granted under the Tidewater Inc. 2001 Stock Incentive Plan in transaction exempt under Rule 16b-3. The Plan pursuant to which the reported option was granted provides for tax withholding rights. The option vests on March 30, 2005.
Stephen Dick, by: Michael Goldblatt, Agent and Attorney-in-Fact
2005-04-01