<?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>0001197253</rptOwnerCik>
            <rptOwnerName>TAYLOR DEAN E</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>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman, CEO &amp; President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3506</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>55.82</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>53655</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-03-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>55000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>108655</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>4131</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>As Custodian for Children</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3618</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trustee</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
                <footnoteId id="F6"/>
            </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>55000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F6"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-03-29</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>55000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>55000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Withholding of shares to pay tax.</footnote>
        <footnote id="F2">Includes 34 shares acquired pursuant to dividend reinvestment plan.</footnote>
        <footnote id="F3">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="F4">As Custodan for Children</footnote>
        <footnote id="F5">Acquired on a periodic basis by the Trustee of Tidewater 401(0K Savings Plan. Includes shares acquired for my account through February 28, 2006.</footnote>
        <footnote id="F6">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>Dean Taylor, by: Michael 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
0001197253
TAYLOR DEAN E
C/O TIDEWATER INC.
601 POYDRAS ST., SUITE 1900
NEW ORLEANS
LA
70130
1
1
0
0
Chairman, CEO & President
Common Stock
2006-03-29
4
F
0
3506
55.82
D
53655
D
Common Stock
2006-03-29
4
A
0
55000
A
108655
D
Common Stock
4131
I
As Custodian for Children
Common Stock
3618
I
By Trustee
Stock Option (Right to Buy)
55.76
2006-03-29
4
A
0
55000
A
2016-03-29
Common Stock
55000
55000
D
Withholding of shares to pay tax.
Includes 34 shares acquired pursuant to dividend reinvestment plan.
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.
As Custodan for Children
Acquired on a periodic basis by the Trustee of Tidewater 401(0K Savings Plan. Includes shares acquired for my account 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.
Dean Taylor, by: Michael Goldblatt, Agent and Attorney-in-Fact
2006-03-31