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

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-03-30</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197247</rptOwnerCik>
            <rptOwnerName>LOUSTEAU J KEITH</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>Exec. V. P., CFO, &amp; Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7000</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>4443</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>28.05</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>17500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-03-30</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-03-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>17500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17500</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 in 3 annual installments of 50%, 25%, and 25% commencing on or about March 30, 2006.</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 February 29, 2004.</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 in 3 equal annual installments beginning on March 30, 2005.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>J. Keith Lousteau, by: Michael Goldblatt, Agent and Attorney-in-Fact</signatureName>
        <signatureDate>2004-04-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0201
4
2004-03-30
0000098222
TIDEWATER INC
TDW
0001197247
LOUSTEAU J KEITH
C/O TIDEWATER INC.
601 POYDRAS ST., SUITE 1900
NEW ORLEANS
LA
70130
0
1
0
0
Exec. V. P., CFO, & Treasurer
Common Stock
2004-03-30
4
A
0
7000
A
7000
D
Common Stock
4443
I
By Trustee
Stock Option (Right to Buy)
28.05
2004-03-30
4
A
0
17500
A
2005-03-30
2014-03-30
Common Stock
17500
17500
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 in 3 annual installments of 50%, 25%, and 25% commencing on or about March 30, 2006.
Acquired on a periodic basis by the Trustee of the Tidewater Inc. 401(k) Savings Plan. Includes shares acquired for my account through February 29, 2004.
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 in 3 equal annual installments beginning on March 30, 2005.
J. Keith Lousteau, by: Michael Goldblatt, Agent and Attorney-in-Fact
2004-04-01