Exhibit 10.1

SEVENTH AMENDMENT TO

THIRD AMENDED AND RESTATED

UNDERWRITING AND CONTINUING INDEMNITY AGREEMENT

THIS SEVENTH AMENDMENT TO THIRD AMENDED AND RESTATED UNDERWRITING AND CONTINUING
INDEMNITY AGREEMENT, dated as of November 11, 2011 (this “Amendment”), is
entered into by and among (i) GREAT LAKES DREDGE & DOCK CORPORATION, a Delaware
corporation (“HOLDINGS”), and the SUBSIDIARIES of HOLDINGS signatories hereto
(collectively with HOLDINGS, the “INDEMNITORS”), (ii) TRAVELERS CASUALTY AND
SURETY COMPANY, a Connecticut corporation (“TCASC”), and (iii) TRAVELERS
CASUALTY AND SURETY COMPANY OF AMERICA, a Connecticut corporation (“TRAVELERS
AMERICA” and together with TCASC, “TRAVELERS”).

W I T N E S S E T H:

WHEREAS, the INDEMNITORS and TRAVELERS are parties to a certain Third Amended
and Restated Underwriting and Continuing Indemnity Agreement dated as of
December 22, 2003, as amended, supplemented or otherwise modified from time to
time (including, for the avoidance of doubt, that certain Rider Concerning
Additional Bonds dated December 31, 2010) (as so amended, supplemented and
modified, the “Agreement”);

WHEREAS, the INDEMNITORS have requested TRAVELERS to amend the Agreement; and

WHEREAS, TRAVELERS is willing to amend the Agreement as provided herein, subject
to the terms and conditions set forth herein;

NOW, THEREFORE, in consideration of the premises, and intending to be legally
bound hereby, the INDEMNITORS and TRAVELERS hereby agree as follows:

1. DEFINED TERMS.

Capitalized terms used herein shall, unless otherwise defined herein, have the
meanings provided in the Agreement.

2. AMENDMENTS TO AGREEMENT.

Subject to satisfaction of the conditions set forth in Section 3 of this
Amendment, the Agreement is hereby amended as follows:

(a) Article VI of the Agreement is hereby amended by deleting Section 6.24
thereof in its entirety.

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3. CONDITIONS PRECEDENT.

The provisions of this Amendment shall be effective upon receipt by TRAVELERS of
the documents listed below:

(b) this Amendment duly executed by all parties hereto.

4. REPRESENTATIONS AND WARRANTIES.

To induce TRAVELERS to enter into this Amendment, the INDEMNITORS represent and
warrant to TRAVELERS as of the date hereof and after giving effect to this
Amendment that:

(c) The representations and warranties contained in Article V of the Agreement,
in Section 4 of each SECURITY AGREEMENT (A/R), in Section 4 of each SECURITY
AGREEMENT (EQUIPMENT), in Section 4 of the PLEDGE AGREEMENT and in Article I of
each of the VESSEL MORTGAGES, are correct in all material respects on and as of
the date hereof as though made on and as of such date except to the extent
stated to relate to an earlier date, in which case such representation and
warranty shall be correct as of such earlier date.

(d) No EVENT OF DEFAULT has occurred and is continuing.

5. GENERAL.

(e) As hereby modified, the Agreement shall remain in full force and effect and
is hereby ratified, approved and confirmed in all respects.

(f) This Amendment shall be binding upon and shall inure to the benefit of the
parties hereto and their respective successors and assigns.

(g) This Amendment may be executed in any number of counterparts and by the
different parties on separate counterparts, and each such counterpart shall be
deemed to be an original, but all such counterparts shall together constitute
but one and the same Amendment.

(h) HOLDINGS acknowledges and agrees that any expense incurred by TRAVELERS in
connection herewith and any other documents referenced herein (if any) and the
transactions contemplated hereby, including reasonable legal fees and
out-of-pocket costs and expenses of outside counsel, shall be fully paid or
reimbursed by HOLDINGS.

[Signature Pages Follow]

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IN WITNESS WHEREOF, this Amendment has been duly executed by the parties as of
the date first written above.

 

GREAT LAKES DREDGE & DOCK CORPORATION

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck   Title:   President
and Chief Financial Officer

 

GREAT LAKES DREDGE & DOCK COMPANY, LLC

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck   Title:   President
and Chief Financial Officer

 

LYDON DREDGING & CONSTRUCTION COMPANY, LTD.

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck  

Title:    Executive Vice President and Chief Operating Officer

 

FIFTY-THREE DREDGING CORPORATION

By:   /s/ Paul E. Dinquel           Name: Paul E. Dinquel   Title:   Vice
President

 

DAWSON MARINE SERVICES COMPANY

By:   /s/ Catherine Hoffman           Name: Catherine Hoffman   Title:
  President

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GREAT LAKES DREDGE & DOCK ENVIRONMENTAL, INC. (f/k/a GREAT LAKES CARIBBEAN
DREDGING, INC.)

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck  

Title:   Senior Vice President and Chief Financial Officer

 

NASDI, LLC

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck   Title:  Vice
President

 

NASDI HOLDINGS CORPORATION

By:   /s/ Bruce J. Biemeck           Name: Bruce J. Biemeck  

Title:   Vice President and Chief Financial Officer

 

YANKEE ENVIRONMENTAL SERVICES, LLC By:   /s/ Bruce J. Biemeck           Name:
Bruce J. Biemeck  

Title:   Vice President and Chief Financial Officer

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TRAVELERS CASUALTY AND SURETY COMPANY

By:   /s/ Michael Damewood            Name: Michael Damewood  

Title:   Attorney-in-Fact

 

TRAVELERS CASUALTY AND SURETY COMPANY OF AMERICA

By:   /s/ Michael Damewood            Name: Michael Damewood  

Title:   Attorney-in-Fact