43 U.S.C. § 36b

The Secretary of the Interior may, on behalf of the United States and for use by the United States Geological Survey in gaging streams and underground water resources, acquire lands by donation or when funds have been appropriated by Congress by purchase or condemnation, but not in excess of ten acres for any one stream gaging station or observation well site. For the same purpose the Secretary of the Interior may obtain easements, licenses, rights-of-way, and leases limited to run for such a period of time or term of years as may be required for the effective performance of the function of gaging streams and underground water resources: Provided , That nothing in this section shall be construed as affecting or intended to affect or in any way to interfere with the laws of any State or Territory relating to the control, appropriation, use, or distribution of water used in irrigation, or any vested right acquired thereunder, and the Secretary of the Interior, in carrying out the provisions of this section, shall proceed in conformity with such laws, and nothing in this section shall in any way affect any right of any State or of the Federal Government or of any landowner, appropriator, or user of water, in, to, or from any interstate stream or the waters thereof.