Big Stone Lake

Big Stone Lake is a long, narrow freshwater lake and reservoir on the border between western Minnesota and northeastern South Dakota. It covers 12,610 acres, runs 26 miles from end to end, averages about 1 mile wide, and is at most 16 feet deep. Ortonville, Minnesota, and Big Stone City, South Dakota, sit at its southern tip, and Browns Valley, Minnesota, is at its northern tip. The lake formed at the end of the last ice age, when glacial Lake Agassiz drained through the Traverse Gap into Glacial River Warren. That river's valley now holds the lake. The Little Minnesota River feeds it from the north, and the lake is the source of the Minnesota River, which flows 332 miles to the Mississippi. The Upper Minnesota River Watershed District runs the Big Stone Lake/Whetstone control structure, built in 1987 just below the foot of the lake. The district holds a summer pool of 968 to 968.3 feet project datum and lowers the lake to about 967 feet each October for spring flood protection.

The lake has 12 public accesses. On the Minnesota side, the City of Ortonville manages ramps in Ortonville, and the DNR Division of Parks and Trails manages ramps including Meadowbrook, Kanne, Mallard Point, Hornsteins and Bonanza. Big Stone Lake State Park has two sections 12 miles apart: the Bonanza Area in the north and the Meadowbrook Area in the south. Zebra mussels were confirmed in the lake in October 2023, on docks from both the Minnesota and South Dakota shores. Minnesota law requires watercraft and trailers to be cleaned of aquatic plants and prohibited invasive species and drain plugs to be left out during transport. Docks and lifts must dry for 21 days before being moved to another water body.

Walleye, northern pike and bluegill are popular game fish, and the lake holds more than 30 other species. The Whetstone River was diverted toward the lake in the 1930s to add water during droughts.