Minn. Stat. § 103G.531: DAM PERMIT EXCEPTIONS.

Subdivision 1. Exemption for structures constructed before July 1, 1937.

This chapter does not authorize the commissioner to require a permit for the original construction of dams, reservoirs, or control works in existence on and before July 1, 1937.

Subd. 2. Minor dam exclusion.

The commissioner shall adopt rules that exclude minor dams such as those less than six feet in height or that impound less than 50 acre-feet of water storage at maximum storage elevations from permit requirements. The rules do not apply to a barrier six feet or less in height, regardless of storage capacity, or to a barrier creating a storage capacity at maximum water storage elevation of 15 acre-feet or less, regardless of height.