Idaho Code § 42-2947
The whole or any portion of any natural watercourse which drains any district established under this chapter, or the whole or any portion of any ditch or drainage system already constructed or partially constructed prior to the passage of this chapter, or which may be constructed subsequent thereto, may be improved and completed as a system under the provisions of this chapter: provided, that the owner or owners of any land upon or in which any drainage system has been established or constructed in whole or in part or which may hereafter be constructed in whole or in part, may take advantage of the provisions of this chapter to organize same as a drainage district, for the purpose of completing same or for the purpose of making provision for the payment or funding of any indebtedness incurred in the construction of such system, or either; and providing for the maintenance thereof. The procedure to be followed in such case shall be the same as is herein provided for the organization of a drainage district in the first instance to the extent that same is applicable to the situation: provided, that the necessary changes and substitutions therein may be made: provided further, that in the improvement of any natural watercourse, the rights of the public therein for the purpose of navigation shall not be in any wise impaired.
Idaho Code § 42-2947