The River Lymn is a river in Lincolnshire, England. It rises in the Wolds on the eastern slope of Castcliffe Hill in Fulletby parish. It flows south-eastwards to the Lincolnshire Marsh, where it becomes known as the Steeping River on the boundary of Great Steeping parish. The main channel is supplemented by the Wainfleet Relief Channel as it passes Wainfleet All Saints, and the relief channel is joined by the old course of the Lymn. Once the two channels rejoin, there are three flood defence structures to protect the region from flooding by the North Sea.

The Lincolnshire Wolds are a range of low hills in the county of Lincolnshire, England which run roughly parallel with the North Sea coast, from the Humber Estuary in the north-west to the edge of the Lincolnshire Fens in the south-east. A large part of the Wolds are a designated Area of Outstanding Natural Beauty (AONB), and form the highest land in eastern England between Yorkshire and Kent.