Minn. Stat. § 541.115: ACTIONS RELATING TO MAINTENANCE OF WATER LEVELS.

No action or proceeding against the state of Minnesota or its officers or agents shall be maintained on account of the construction, reconstruction, operation, or maintenance of any dam or appurtenant structures designed to maintain water levels above natural ordinary high or on account of the maintenance of such levels, where such levels have been maintained for a period of 15 years or more prior to January 1, 1941.