The Car Dyke was, and to a large extent still is, a long ditch which runs along the western edge of the Fens in eastern England for a distance of over 57 miles (92 km). It is generally accepted as being of Roman age and, for many centuries, to have been taken as marking the western edge of the Fens. The name derives from carr, a fourteenth-century word for marsh or drained land.

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.