Big Stone Lake is the source of the Minnesota River, which flows 332 miles (534 km) to the Mississippi River.
Flow from the lake to the Minnesota River is regulated by the Big Stone Lake Dam, built in 1937 at the lake’s southern end.
It [Whetstone River] enters the Minnesota River at Ortonville, Minnesota, about 0.25 mi (0.4 km) after crossing the state line and just downstream of the Minnesota’s emergence from Big Stone Lake.
Big Stone Lake is the source of the Minnesota River, which flows 332 miles (534 km) to the Mississippi River.
Big Stone Lake (Wikipedia) Big Stone Lake (Dakota: Íŋyaŋ Tháŋka Bdé) is a long, narrow freshwater lake and reservoir on the border between western Minnesota and northeastern South Dakota in the United States.