Big Marsh Creek is a tributary of Crescent Creek in Klamath County, in the U.S. state of Oregon. The creek flows generally north from its source upstream of Big Marsh, south of Crescent Lake Junction on the eastern side of the Cascade Range. All of Big Marsh Creek and of Crescent Creek are parts of the National Wild and Scenic Rivers System. In turn, Crescent Creek is a tributary of the Little Deschutes River, of which in the same general area are also part of the national system.