D.C. Code § 10-162

The Mayor of the District of Columbia is hereby authorized and permitted to construct a beach and dressing houses upon the east shore of the tidal reservoir against the Washington Monument Grounds, and to maintain the same for the purpose of free public bathing, under such regulations as the Council of the District of Columbia shall deem to be for the public welfare; and the Secretary of the Army is requested to permit such use of the public domain as may be required to accomplish the objects above set forth.