Exhibit 10.1

AMENDMENT NO. 4

TO CREDIT AGREEMENT

THIS AMENDMENT NO. 4 TO CREDIT AGREEMENT (this “Amendment”), dated as of
September 7, 2011, is made by and among Great Lakes Dredge & Dock Corporation
(the “Borrower”), the other “Loan Parties” from time to time party to the Credit
Agreement referred to and defined below (together with the Borrower, the “Loan
Parties”), the Lenders (as defined below) signatory hereto and Bank of America,
N.A. (successor by merger to LaSalle Bank National Association) as Swing Line
Lender, Issuing Lender and Administrative Agent (in such capacity, the
“Administrative Agent”). Capitalized terms used herein and not otherwise defined
herein shall have the meanings ascribed to such terms in the Credit Agreement
referred to and defined below.

W I T N E S S E T H:

WHEREAS, the Borrower, the other Loan Parties, the financial institutions from
time to time party thereto (collectively, the “Lenders”), the Administrative
Agent and the Issuing Lender have entered into that certain Credit Agreement,
dated as of June 12, 2007 (as amended, restated, supplemented or otherwise
modified prior to the date hereof, the “Credit Agreement”), pursuant to which,
among other things, the Lenders have agreed to provide, subject to the terms and
conditions contained therein, certain loans and other financial accommodations
to the Borrower;

WHEREAS, the Borrower has requested that the Majority Lenders, and subject to
the terms and conditions set forth herein, the Majority Lenders have agreed to,
amend certain provisions of the Credit Agreement;

NOW, THEREFORE, in consideration of the foregoing premises, the terms and
conditions stated herein and other valuable consideration, the receipt and
sufficiency of which are hereby acknowledged by the Borrower, the other Loan
Parties, the Majority Lenders and the Administrative Agent, such parties hereby
agree as follows:

1. Amendments to Credit Agreement. Subject to the satisfaction of each of the
conditions set forth in Section 2 of this Amendment, the Credit Agreement is
hereby amended as follows:

(a) Section 6.1(n) of the Credit Agreement is hereby amended and restated in its
entirety as follows:

(n) Bonding Agreement. The Borrower will take all action necessary to maintain
the Bonding Agreement in full force and effect and will promptly notify the
Administrative Agent of any supplement, replacement or amendment thereof;
provided that, subject to Section 6.1(p) and the Zurich Agreement becoming
effective, the Travelers Agreement may be terminated.

(b) Section 6.1(p) of the Credit Agreement is hereby amended to insert the
following sentence at the end of such section:

The Borrower shall (x) promptly notify the Administrative Agent of the
termination of the Travelers Agreement, payment in full of all obligations
thereunder and the expiration of all bonds issued thereunder and (y) within
ninety (90) days (or such later date as the Administrative Agent shall determine
in its sole discretion) of the occurrence of the last of such events, furnish to
the Administrative Agent evidence, reasonably satisfactory to the Administrative
Agent, of the release and termination of all Liens of Travelers granted pursuant
to the Travelers Agreement. Upon such release and termination by Travelers, the
Liens granted to the Administrative Agent securing the Obligations for the
benefit of the Secured Parties and described in the foregoing clauses (ii),
(iii) and (iv) shall thereupon and thereafter become and remain perfected first
priority liens (or preferred Ship Mortgages, as the case may be).

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(c) Subclause (E) of Section 6.2(e) of the Credit Agreement is hereby amended
and restated in its entirety as follows:

(E) the Travelers Agreement, the Wells Fargo Documents, the Intercreditor
Agreement, the Note Indenture and any agreement, document or instrument
evidencing or governing any Permitted Note Refinancing;

(d) Section 6.2(h)(vii) of the Credit Agreement is hereby amended and restated
in its entirety as follows:

(vii) (A) Liens granted to sureties under the Bonding Agreement (other than the
Zurich Agreement), to the extent permitted by the Intercreditor Agreement and
(B) Liens granted to sureties under the Zurich Agreement pursuant to the terms
of the Zurich Agreement as in effect on the date hereof, and Liens granted by
additional indemnitors subsequently joined thereto and having the same scope as
the Liens granted by the existing indemnitors under the terms of the Zurich
Agreement as in effect on the date hereof.

(e) Section 7.1(d) of the Credit Agreement is hereby amended and restated in its
entirety as follows:

(d) Default as to Other Debt. (i) Default in the payment when due subject to any
applicable grace period (whether by scheduled maturity, required prepayment,
required redemption, acceleration, demand or otherwise) on any Debt (other than
the Obligations), individually or in the aggregate, having an outstanding
principal amount in excess of $5,000,000, of or guaranteed by, any Loan Party or
Subsidiary of the Borrower; or (ii) any breach, default or event of default
shall occur, or any other event shall occur or condition shall exist, under any
instrument, agreement or indenture pertaining thereto, if the effect thereof,
after giving effect to any applicable grace or cure period, is to accelerate, or
permit the holder(s) of such Debt to accelerate the maturity of such Debt, or
require a mandatory redemption or repurchase of such Debt prior to its scheduled
redemption or repurchase; or (iii) any such Debt or any Debt under the Wells
Fargo Agreement shall be declared due and payable or required to be prepaid
(other than by a regularly scheduled required prepayment (including, without
limitation, pursuant to Section 3.1 (or any comparable section) of the Wells
Fargo Agreement)), repurchased or redeemed prior to the originally stated
maturity thereof; or (iv) the holder of any Lien related to a Debt in excess of
$5,000,000 or the holder of any Lien in respect of Debt under the Wells Fargo
Agreement shall commence foreclosure of such Lien; or (v) an “Event of Default”
shall have occurred under and as defined in any Bonding Agreement after giving
effect to any applicable cure periods and any waivers thereof; or (vi) an “Event
of Default” shall have occurred under and as defined in Section 6.01 of the Note
Indenture (or an event of default shall have occurred with respect to any
Permitted Note Refinancing); or (vii) an “Event of Default” shall have occurred
under and as defined in Section 10.1 (or any comparable section) of the Wells
Fargo Agreement.

(f) Section 7.1(k)(ii) of the Credit Agreement is hereby amended and restated in
its entirety as follows:

(ii) (x) Travelers provides notice to the Administrative Agent (pursuant to
Section 4.4 of the Intercreditor Agreement) of any breach or default under any
bonded contract or under the Travelers Agreement and, as a result thereof,
Travelers has taken action pursuant to Section 4.1(a) of the Intercreditor
Agreement, or (y) any “Surety” under and as defined in the Zurich Agreement
shall perfect any Lien under the Zurich Agreement and such Lien remains
perfected for a period of fifteen (15) days or more, or provides notice to the
Borrower or any Subsidiary of the Borrower of any breach or default under any
bonded contract or under the Zurich Agreement, or enforces any Lien under the
Zurich Agreement, or exercises any remedies as a secured party with respect to
such Liens; or.

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(g) Section 8.10 of the Credit Agreement is hereby amended to insert the new
clause (d) in proper alphabetical order as follows:

(d) Equipment Utilization Agreement. Each Lender from time to time party hereto
authorizes and consents, by its execution hereof or by the Assignment and
Acceptance by which it became a Lender, to the Administrative Agent’s entering
into the Equipment Utilization Agreement on such Lender’s behalf and taking all
actions taken, required or permitted to be taken by the Administrative Agent
thereunder.

(h) The definition of “Bonding Agreement” set forth on Schedule I to the Credit
Agreement is hereby amended and restated as follows:

“Bonding Agreement” means, collectively, (i) the Travelers Agreement and any
supplement thereto or replacement thereof, and any similar contractual
arrangement (other than the Zurich Agreement) with providers of bid, performance
or payment bonds, each of which supplement, replacement or similar arrangement
being subject to the Intercreditor Agreement, and (ii) the Zurich Agreement.

(i) Schedule I to the Credit Agreement is hereby amended to insert the following
new definitions in proper alphabetical order as follows:

“Equipment Utilization Agreement” means the Equipment Utilization Agreement,
dated as of September 7, 2011, among the Borrower, Great Lakes and the other
Subsidiaries of the Borrower, the Administrative Agent and Zurich American
Insurance Company, Fidelity and Deposit Company of Maryland, Colonial American
Casualty and Surety Company and American Guarantee and Liability Insurance, as
sureties thereunder, substantially in the form delivered to the Administrative
Agent on September 7, 2011, and as may be amended from time to time to join
additional indemnitors thereunder.

“Zurich Agreement” means that certain Agreement of Indemnity, dated as of
September 7, 2011, executed by the Borrower, Great Lakes and the other
Subsidiaries of the Borrower as “Contractors” and Indemnitors”, in favor of
Zurich American Insurance Company and its subsidiaries and affiliates, as
amended, restated, supplemented or otherwise modified from time to time in
accordance with the terms hereof.

2. Effectiveness of this Amendment; Conditions Precedent. The provisions of
Section 2 of this Amendment shall be deemed to have become effective as of the
date first written above (the “Effective Date”), but such effectiveness shall be
expressly conditioned upon the Administrative Agent’s receipt of each of the
following, in each case, in form and substance reasonably acceptable to the
Administrative Agent:

(a) counterparts of this Amendment executed by Authorized Officers of the
Borrower, the other Loan Parties and the Majority Lenders;

(b) a fully executed copy of the Zurich Agreement and the Equipment Utilization
Agreement in the forms delivered to the Administrative Agent on September 7,
2011; and

(c) for the account of each Lender executing and delivering a counterpart
signature page to this Amendment before 10:00 a.m. (Chicago time) on
September 7, 2011 (collectively, the “Consenting Lenders”), payment in full from
the Borrower, in immediately available funds, of an amendment fee in an amount
equal to 0.05% of such Consenting Lender’s Revolving Commitment.

3. Representations and Warranties.

(a) The Borrower and each other Loan Party hereby represents and warrants that
this Amendment and the Credit Agreement as amended hereby (collectively, the
“Amendment Documents”) constitute legal, valid and binding obligations of the
Borrower and the other Loan Parties enforceable against the Borrower and the
other Loan Parties in accordance with their terms.

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(b) The Borrower and each other Loan Party hereby represents and warrants that
its execution and delivery of this Amendment, and the performance of the
Amendment Documents, have been duly authorized by all proper corporate or
limited liability company action, do not violate any provision of its
organizational documents, will not violate any law, regulation, court order or
writ applicable to it, and will not require the approval or consent of any
governmental agency, or of any other third party under the terms of any contract
or agreement to which it or any of its Affiliates is bound (which has not been
previously obtained), including without limitation, the Bonding Agreement, the
Wells Fargo Documents and the Indenture, dated as of January 28, 2011, among
Wells Fargo Bank, National Association, as trustee, the Borrower and the
Subsidiary Guarantors.

(c) The Borrower and each other Loan Party hereby represents and warrants that,
both before and after giving effect to the provisions of this Amendment, (i) no
Default or Event of Default has occurred and is continuing or will have occurred
and be continuing and (ii) all of the representations and warranties of the
Borrower and each other Loan Party contained in the Credit Agreement and in each
other Loan Document (other than representations and warranties which, in
accordance with their express terms, are made only as of an earlier specified
date) are, and will be, true and correct as of the date of its execution and
delivery hereof or thereof in all material respects as though made on and as of
such date.

4. Reaffirmation, Ratification and Acknowledgment. The Borrower and each other
Loan Party hereby (a) ratifies and reaffirms all of its payment and performance
obligations, contingent or otherwise, and each grant of security interests and
liens in favor of the Administrative Agent, under each Loan Document to which it
is a party, (b) agrees and acknowledges that such ratification and reaffirmation
is not a condition to the continued effectiveness of such Loan Documents and
(c) agrees that neither such ratification and reaffirmation, nor the
Administrative Agent’s, or any Lender’s solicitation of such ratification and
reaffirmation, constitutes a course of dealing giving rise to any obligation or
condition requiring a similar or any other ratification or reaffirmation from
the Borrower or such other Loan Parties with respect to any subsequent
modifications to the Credit Agreement or the other Loan Documents. As modified
hereby, the Credit Agreement is in all respects ratified and confirmed, and the
Credit Agreement as modified by this Amendment shall be read, taken and so
construed as one and the same instrument. Each of the Loan Documents shall
remain in full force and effect and are hereby ratified and confirmed. Neither
the execution, delivery nor effectiveness of this Amendment shall operate as a
waiver of any right, power or remedy of the Administrative Agent or the Lenders,
or of any Default or Event of Default (whether or not known to the
Administrative Agent or the Lenders), under any of the Loan Documents. From and
after the effectiveness of this Amendment, (x) each reference in the Credit
Agreement to “this Agreement,” “hereunder,” “hereof,” “herein” or words of like
import shall mean and be a reference to the Credit Agreement, as amended hereby
and (y) all references to the Credit Agreement appearing in any other Loan
Document, or any other document, instrument or agreement executed and/or
delivered in connection therewith, shall mean and be a reference to the Credit
Agreement, as amended hereby.

5. Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO ITS
CONFLICTS OF LAW PRINCIPLES (OTHER THAN THE PROVISIONS OF 5-1401 AND 5-1402 OF
THE NEW YORK GENERAL OBLIGATIONS LAW).

6. Administrative Agent’s Expenses. The Borrower hereby agrees to promptly
reimburse the Administrative Agent for all of the reasonable out-of-pocket
expenses, including, without limitation, attorneys’ and paralegals’ fees, it has
heretofore or hereafter incurred or incurs in connection with the preparation,
negotiation and execution of this Amendment and the other documents, agreements
and instruments contemplated hereby.

7. Counterparts. This Amendment may be executed in counterparts, each of which
shall be an original and all of which when together shall constitute one and the
same agreement among the parties. Delivery of any executed counterpart of a
signature page of this Amendment by facsimile or other electronic imaging shall
be effective as delivery of a manually executed counterpart hereof.

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IN WITNESS WHEREOF, this Amendment has been duly executed as of the day and year
first above written.

 

GREAT LAKES DREDGE & DOCK CORPORATION By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

President & CFO

GREAT LAKES DREDGE & DOCK ENVIRONMENTAL, INC. By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

Senior Vice President & CFO

GREAT LAKES DREDGE & DOCK COMPANY, LLC By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

President & CFO

DAWSON MARINE SERVICES COMPANY By:  

/s/ Catherine Hoffman

Name:  

Catherine Hoffman

Title:  

President

NASDI HOLDINGS CORPORATION By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

Vice President & CFO

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NASDI, LLC By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

Vice President

FIFTY-THREE DREDGING CORPORATION By:  

/s/ Paul Dinquel

Name:  

Paul Dinquel

Title:  

Vice President

YANKEE ENVIRONMENTAL SERVICES, LLC By:  

/s/ Bruce J. Biemeck

Name:  

Bruce J. Biemeck

Title:  

Vice President & CFO

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BANK OF AMERICA, N.A. (successor by merger to LaSalle Bank National
Association), as Administrative Agent By:  

/s/ Bozena Janociak

Name:  

Bozena Janociak

Title:  

Assistant Vice President

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BANK OF AMERICA, N.A. (successor by merger to LaSalle Bank National
Association), as a Lender By:  

/s/ Jonathan M. Phillips

Name:  

Jonathan M. Phillips

Title:  

Senior Vice President

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GENERAL ELECTRIC CAPITAL CORPORATION, as a Lender By:  

/s/ Jennifer Pricco

Name:  

Jennifer Pricco

Title:  

Duly Authorized Signatory

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FIFTH THIRD BANK, as a Lender By:  

/s/ Neil G. Mesch

Name:  

Neil G. Mesch

Title:  

Vice President

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PNC BANK, NATIONAL ASSOCIATION (successor to National City Bank), as a Lender
By:  

/s/ Jon R. Hinard

Name:  

Jon R. Hinard

Title:  

Senior Vice President

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RBS CITIZENS, N.A. (successor by merger to Charter One Bank), as a Lender By:  

/s/ Mark A. Wegener

Name:  

Mark A. Wegener

Title:  

Senior Vice President

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WELLS FARGO BANK, NATIONAL ASSOCIATION, as a Lender By:  

/s/ Sushim R. Shah

Name:  

Sushim R. Shah

Title:  

Senior Relationship Manager & VP

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MB FINANCIAL BANK, as a Lender By:  

/s/ Henry Wesser

Name:  

Henry Wesser

Title:  

Vice President