Sec Form 4 Filing - JOHANSON DAVID @ Great Lakes Dredge & Dock CORP - 2026-04-01

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person JOHANSON DAVID 2. Issuer Name and Ticker or Trading Symbol Great Lakes Dredge & Dock CORP [ GLDD] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP-Project Acquisition & Ops (Last) (First) (Middle) C/O GREAT LAKES DREDGE & DOCK CORP., 9811 KATY FREEWAY, SUITE 1200 3. Date of Earliest Transaction (MM/DD/YY) 04/01/2026 (Street) HOUSTON, TX77024 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/25/2026 A( 1 ) 521.257 A $ 10.821 ( 2 ) 119,737.5164 D Common Stock 04/01/2026 A( 3 ) 71,860 ( 3 ) A 191,597.5164 D Common Stock 04/01/2026 U 191,597.5164 ( 4 ) ( 5 ) D 0 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other JOHANSON DAVID C/O GREAT LAKES DREDGE & DOCK CORP. 9811 KATY FREEWAY, SUITE 1200 HOUSTON, TX77024 SVP-Project Acquisition & Ops Signatures /s/Vivienne R. Schiffer, by Power of Attorney 04/01/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares were acquired under the Great Lakes Dredge & Dock Corporation 2025 Employee Stock Purchase Plan ("ESPP"). ( 2 )In accordance with the ESPP, these shares were purchased at a price equal to 85% of the closing price of the Issuer's common stock on December 1, 2025. ( 3 )Pursuant to the Merger Agreement (as defined in footnote 2 below), at the Effective Time (as defined in footnote 2 below), these performance-based restricted stock units fully vested, with the number earned or deemed earned as set forth in the Merger Agreement. ( 4 )Pursuant to the Agreement and Plan of Merger (the "Merger Agreement"), dated February 10, 2026, by and among Saltchuk Resources, Inc. ("Parent"), Huron MergeCo, Inc. ("Merger Sub"), and Great Lakes Dredge & Dock Corporation ("Issuer") on April 1, 2026 (the "Effective Time"), Merger Sub merged with and into Issuer, with Issuer surviving as a wholly owned subsidiary of Parent upon consummation of the transactions contemplated by the Merger Agreement. At the Effective Time, each outstanding share of common stock of the Issuer ("Common Stock") was cancelled and converted into the right to receive $17.00 in cash (the "Merger Consideration"), without interest and subject to any required tax withholdings. ( 5 )Includes 103,250 restricted stock units ("RSUs"). At the Effective Time, 89,375 outstanding RSUs were canceled and converted into the right to receive an amount in cash equal to the product of the aggregate number of shares of Common Stock underlying such RSUs immediately prior to the Effective Time, multiplied by the Merger Consideration, and 13,515 RSUs were replaced by a cash-based award of equivalent value (based on the Offer Price (as defined in the Merger Agreement)) that is subject to the same time-based vesting conditions as applied to the unvested portion of such award prior to the Effective Time.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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