D.C. Code § 10-152

For the purpose of preventing the pollution and obstruction of Rock Creek and of connecting Potomac Park with the Zoological Park and Rock Creek Park, a commission, to be composed of the Secretary of the Treasury, the Secretary of Defense, and the Secretary of Agriculture, is authorized and directed to acquire, by purchase, condemnation or otherwise, such land and premises as were not, on March 4, 1913, the property of the United States in the District of Columbia shown on the map on file in the Office of the Mayor of the District of Columbia, dated May 17, 1911, and lying on both sides of Rock Creek, including such portion of the creek bed as may be in private ownership, between the Zoological Park and Potomac Park; and the sum of $1,300,000 is hereby authorized to be expended toward the acquirement of such lands. All lands belonging, on March 4, 1913, to the United States or to the District of Columbia lying within the exterior boundaries of the land to be acquired by this section as shown and designated on said map are appropriated to and made a part of the parkway herein authorized to be acquired. One-half of the cost of the said lands shall be reimbursed to the Treasury of the United States out of the revenues of the District of Columbia in 8 equal annual installments, with interest at the rate of 3 per centum per annum, upon the deferred payments.