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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-03-29</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>2006-03-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>18000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>45693</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1444</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.82</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>44249</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>2817</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trustee</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
                <footnoteId id="F4"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>55.76</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-03-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>18000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-03-29</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock awarded under the Tidewater Inc. 2001 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 the change in Economic Value Added (EVA) meets or exceeds annual targeted improvement. EVA equals after-tax operating profits less a charge for debt and equity capital. Capital is charged at a rate equal to the weighted average cost of debt and equity. Any unvested restricted stock will automatically vest on March 29, 2010.</footnote>
        <footnote id="F2">Withholding of shares to pay tax.</footnote>
        <footnote id="F3">Acquired on a periodic basis by the Trustee of Tidewater 401(k) Savings Plan.  Includes shares acquired through February 28, 2006.</footnote>
        <footnote id="F4">Stock option granted pursuant to 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 on March 29, 2006, March 29, 2008, and March 29, 2009.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Stephen W. Dick, By: Michael L. Goldblatt, Agent and Attorney-in-Fact</signatureName>
        <signatureDate>2006-03-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-03-29
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
2006-03-29
4
A
0
18000
A
45693
D
Common Stock
2006-03-30
4
F
0
1444
55.82
D
44249
D
Common Stock
2817
I
By Trustee
Stock Option (Right to Buy)
55.76
2006-03-29
4
A
0
18000
A
2016-03-29
Common Stock
18000
18000
D
Restricted stock awarded under the Tidewater Inc. 2001 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 the change in Economic Value Added (EVA) meets or exceeds annual targeted improvement. EVA equals after-tax operating profits less a charge for debt and equity capital. Capital is charged at a rate equal to the weighted average cost of debt and equity. Any unvested restricted stock will automatically vest on March 29, 2010.
Withholding of shares to pay tax.
Acquired on a periodic basis by the Trustee of Tidewater 401(k) Savings Plan.  Includes shares acquired through February 28, 2006.
Stock option granted pursuant to 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 on March 29, 2006, March 29, 2008, and March 29, 2009.
Stephen W. Dick, By: Michael L. Goldblatt, Agent and Attorney-in-Fact
2006-03-31