33 U.S.C. § 567

Congress consents that the States of Minnesota, North Dakota, and South Dakota, or any two of them, may enter into any agreement or agreements with each other to aid in improving navigation and to prevent and control floods on boundary waters of said States and the waters tributary thereto. And said States, or any two of them, may agree with each other upon any project or projects for the purpose of making such improvements, and upon the amount of money to be contributed by each to carry out such projects. The Secretary of the Army is authorized and directed to make a survey of any project proposed, as aforesaid, by said States, or any two of them, to determine the feasibility and practicability thereof and the expenses of carrying the same into effect and what share of such expenses should be borne by the respective States, local interests, or by the National Government. If the Secretary of the Army approves any such projects, he may authorize the States to make such improvements at their own expense, but under his supervision.