Idaho Code § 42-2810
Any county in which any irrigation or drainage project shall have been established under the provisions of this chapter by order of the board of county commissioners, or which contains any part of the irrigable lands of such projects so established, is hereby authorized to cooperate with the United States and the officers of the interior department and reclamation service for the purpose of furnishing irrigation or drainage, or a more complete or ample water supply by means of reservoirs, canals, or other works, to lands in such county, is authorized to exercise all powers which are granted by chapter 18 of title 43, sections 43-1803 to 43-1828 inclusive of the Idaho Code to irrigation districts, and the board of county commissioners of such county are granted all powers and authorized to do all acts granted or authorized under said sections to be done, exercised or performed by the board of directors of an irrigation district.
Idaho Code § 42-2810