The River Welland is a lowland river in the east of England, some 65 miles (105 km) long. It drains part of the Midlands eastwards to The Wash. The river rises in the Hothorpe Hills, at Sibbertoft in Northamptonshire, then flows generally northeast to Market Harborough, Stamford and Spalding, to reach The Wash near Fosdyke. It is a major waterway across the part of the Fens called South Holland, and is one of the Fenland rivers that were laid out with washlands. There are two channels between widely spaced embankments with the intention that flood waters would have space in which to spread while the tide in the estuary prevented free egress. However, after the floods of 1947, new works such as the Coronation Channel were constructed to control flooding in Spalding, and the washlands are no longer used solely as pasture, but may be used for arable farming.

The Wash is a shallow natural rectangular bay and multiple estuary on the east coast of England, United Kingdom. The bay is an inlet of the North Sea. It is the largest estuary system in the United Kingdom, the largest natural bay in England and one of the most important places of conservation in Europe, with several nature reserves.