Idaho Code § 42-3603
The state of Idaho, by and through the director of the department of lands with the approval of the board of land commissioners, is authorized to enter into reasonable agreements with any authorized federal officer or agency or any other authorized body or person whomsoever, or any combination thereof, in constructing and maintaining or in any other manner whatsoever completing and effectuating any number of "works of improvement" under the said "Watershed Protection and Flood Prevention Act." Provided, however, that no such agreement shall obligate the state of Idaho to bear more than its reasonable share of the cost of such "works of improvement," considering the benefits accruing to the state of Idaho in relation to benefits accruing to others.
Idaho Code § 42-3603