The River Maun is a river in Nottinghamshire, England. Its source lies in Kirkby-in-Ashfield, and from there it flows north east through Mansfield (which takes its name from the river), Edwinstowe and Ollerton, these being the heart of the Sherwood Forest area. It becomes known as Whitewater near the village of Walesby and connects to the River Meden temporarily where the Robin Hood Way crosses them. They diverge, and near Markham Moor it merges again with the River Meden  this time becoming the River Idle. Its main tributaries are Rainworth Water, Vicar Water and Cauldwell Water.