Big Stone Lake

Big Stone Lake, source of the Minnesota River in the U.S., on the Minnesota–South Dakota border, 300 miles (480 km) west-northwest of Minneapolis. Once part of the southern outlet of the extinct glacial Lake Agassiz, its name comes from red granite outcrops in the vicinity. Its waters are impounded in a narrow spillway by the delta of the Whetstone River. The lake is 26 miles (42 km) long and 0.75 to 1.25 miles (1.2 to...