River Idle

River Idle
The road bridge and sluice gate at the junction with the River Trent
Country	England
Basin features
Main source	Confluence of River Maun and River Meden 59 feet (18 m)
River mouth	River Trent 0 ft (0 m)
Tributaries	Left: River Poulter, River Ryton
Physical characteristics
Length	26 miles (42 km)

The River Idle is a river in Nottinghamshire, England. Its source is the confluence of the River Maun and River Meden, near Markham Moor. From there, it flows north through Retford and Bawtry before entering the River Trent at Stockwith near Misterton. The county boundary with South Yorkshire follows the river for a short distance near Bawtry, and the border with Lincolnshire does the same at Idle Stop. Originally, it flowed northwards from Idle Stop to meet the River Don on Hatfield Chase, but was diverted eastwards by drainage engineers in 1628.

Most of the land surrounding the river is a broad flood plain. Between Retford and Bawtry, the floodplain is partly occupied by a number of sand and gravel pits, where exhausted forming public lakes for fishing, while beyond Bawtry, the river is constrained by high flood banks, to allow the low-lying areas to be drained for agriculture. Its main tributaries are the River Poulter and the River Ryton.

The river is navigable to Bawtry, although navigation rights were removed in 1972. It is also important for conservation, with the Idle Washlands and some of the sand and gravel pits of the Idle Valley being designated Sites of Special Scientific Interest.

To the west of the region through which the river flows, the underlying geology is an extensive water-bearing porous rock structure called the Magnesian Limestone aquifer. Magnesian limestone is so named because if contains quantities of the mineral Dolomite, which is rich in Magnesium. Further to the east, this rock is covered by another layer of porous rock called the Triassic Sherwood Sandstone aquifer, which is the major geological component of the area. Continuing eastwards, both are then covered by a layer of Mercia mudstone. Where these aquifers reach the surface, they often supply water to the river system, but can also take water from it. This is affected by the extraction of groundwater, particularly for public water supply, and by fracturing of the aquifers as a result of subsidence caused by deep coal mining.