|Marais des Cygnes River|
Big Osage River, Brush Creek, Grand River, Old Aunt Mary River 
Map of the Osage River watershed including the Marais des Cygnes River
|- location||Lyon County, Kansas|
|- elevation||1,112 ft (339 m)|
|Vernon County, Missouri|
MARAIS DES CYGNES RIVER Latitude and Longitude:
|722 ft (220 m)|
|Length||217 mi (349 km)|
|- location||USGS 06916600 near Kansas- Missouri state line |
|- average||2,189 cu ft/s (62.0 m3/s)|
|- minimum||0 cu ft/s (0 m3/s)|
|- maximum||129,000 cu ft/s (3,700 m3/s)|
|- left||110 Mile Creek, Bull Creek|
|- right||Pottawatomie Creek|
|Watersheds||Marais des Cygnes- Osage- Missouri- Mississippi|
The Marais des Cygnes River (
The Marais des Cygnes is formed about 1 mile north of Reading, Kansas, a city in northern Lyon County, by the confluence of Elm Creek and One Hundred Forty-Two Mile Creek, and flows generally east-southeastwardly through Osage, Franklin, Miami and Linn counties in Kansas, and Bates County in Missouri, past the Kansas towns of Melvern, Quenemo, Ottawa, Osawatomie and La Cygne and through the Marais des Cygnes National Wildlife Refuge. In Missouri, it joins the Little Osage River at the boundary of Bates and Vernon counties to form the Osage River, 6 miles (10 km) west of Schell City.
The Marais des Cygnes River has a history of flooding. One of the first such floods that has been noted is the Great Flood of 1844 known as "Big Water" in Native American legend. Though no measurements were taken, it is estimated to have crested at 40 feet (12 m).
Some of the more notable floods after 1844 include the 1909 flood, cresting at 36.3 feet (11.1 m); the 1915 flood, cresting at 31 feet (9.4 m); the 1928 flood, cresting at 38.65 feet (11.78 m); the 1944 flood, cresting at 36.5 feet (11.1 m); the 1951 flood, cresting at 42.97 feet (13.10 m); and the 2007 flood, cresting at 36.07 feet (10.99 m). 
The Great Flood of 1951 happened in June and July 1951, killing 28 people and causing over $935 million damage (in 1951 dollars). This flood also affected the Kansas, Neosho, and Verdigris river basins.
As a result of the 1951 flood, the U.S. Army Corps of Engineers built levees and flood control systems on the Marais des Cygnes in the 1960s, including massive freestanding gated floodwalls in Ottawa, Kansas. Main Street (Old U.S. Highway 59) in Ottawa has to be detoured or is simply closed down when the gates are shut.
It is most often pronounced Mare D' Zeen river by those who live nearby it.
- "Marais des Cygnes River". Geographic Names Information System. United States Geological Survey. Retrieved 2015-11-05.
- "Water-Data Report 2013 - 06916600 Marais des Cygnes River near Kansas-Missouri State Line, KS" (PDF). U.S. Geological Survey. Retrieved 2015-11-05.
- U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map Archived 2012-04-05 at WebCite, accessed May 31, 2011
- "Archived copy". Archived from the original on 2010-06-15. Retrieved 2010-05-28. Pictures of the Flood of 2007 in La Cygne, KS