Big Muddy River The Big Muddy was not covered by the Wisconsin Glacier, about 70,000 to 10,000 years before present. However, during the melting of that glacier, the level of the Mississippi River was much higher. Water backed up into the Big Muddy Basin, forming a lake much like the artificial Rend Lake but covering a larger area. The ancient lake silted in, forming a flat bottom. After the melting of the Wisconsinan glacier, the level of the Mississippi dropped, allowing the lake to drain. A new channel formed within the old lake bed. This channel meandered in the flat bottom of the
Muddy River (Washington) gauge. Muddy River (Washington) The Muddy River is a stream, about long, southeast of Mount St. Helens in the U.S. state of Washington. The Muddy River flows south–southeast and joins the Lewis River just above the Swift Reservoir. The Lewis River flows west and is a tributary to the Columbia River. The east flank of Mount St. Helens is within the watershed of Muddy Creek. During the 1980 eruption of Mount St. Helens, lahars (volcanically-induced mud and debris flows) swept through its channel. About of stream channels around the volcano were affected by lahars. The United States Forest Service maintains