“ DES MOINES RIVER. The most important river of Iowa. It is formed by the meeting of the east and west forks of the Des Moines in Humboldt County, Iowa. The east fork is the outlet of Okamanpadu Lake, in Emmet County, Iowa; the west fork flows from a chain of lakes among which is Lake Heron, in Jackson County, Minn. (Map: Iowa, D 3) . The Des Moines flows southeasterly across Iowa, and empties into the Mississippi River (q.v.) three miles below Keokuk. It is 550 miles long, drains an area of 14,500 square miles, and is navigable for nearly 100 miles. ”