Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 91, § 10D

No person shall be denied access during daylight hours to commonwealth tidelands across any land available to the public for swimming or recreation which is owned or controlled by the commonwealth or any of its political subdivisions for the purpose of scuba diving or skin diving which activities are hereby declared to be water dependent uses; provided, however, that if such tidelands are at any time closed to access by the general public, such access by such scuba diver or skin diver shall not be permitted.