The River Idle is a river in Nottinghamshire, England whose source is the confluence of the River Maun and River Meden near Markham Moor. The Idle flows north from its source through Retford and Bawtry before entering the River Trent at West Stockwith. Its main tributaries are the River Poulter and the River Ryton. The river is navigable to Bawtry, and there is a statutory right of navigation to Retford. Most of the land surrounding the river is a broad flood plain and the river is important for conservation, with Sites of Special Scientific Interest being designated along its course.

Nottinghamshire is a ceremonial county in the East Midlands of England. The county borders South Yorkshire to the north-west, Lincolnshire to the east, Leicestershire to the south, and Derbyshire to the west. The largest settlement is the city of Nottingham (323,632).