Wis. Stat. § 31.31: Dams on nonnavigable streams.

Any person may erect and maintain upon that person’s land, and, with the consent of the owner, upon the land of another, a water mill and a dam to raise water for working it upon and across any stream that is not navigable in fact for any purpose whatsoever upon the terms and conditions and subject to the regulations hereinafter expressed; and every municipality may exercise the same rights upon and across such streams that they may exercise upon or across streams navigable for any purpose whatsoever.