The Marais des Cygnes River (, , or ) is a principal tributary of the Osage River, about long, in eastern Kansas and western Missouri in the United States. Via the Osage and Missouri rivers, it is part of the watershed of the Mississippi River. The name Marais des Cygnes means "Marsh of the Swans" in French (presumably in reference to the trumpeter swan which was historically common in the Midwest.) The river is notorious for flash flooding. The river is referenced in the song "The River" by Chely Wright.