The Fens, also known as the Fenland, consist of an area of former wetlands in the eastern part of England, stretching around the coast of The Wash from Lincolnshire to Norfolk and reaching into the historic counties of Cambridgeshire, Huntingdonshire, Lincolnshire, Norfolk, Northamptonshire and Suffolk. These former wetlands consisted both of alkaline peat fen and silt freshwater and salt marshes which were virtually all drained by end of the nineteenth century.
The drainage was organized into river drainage, the passing of upland water through the region and internal drainage of the land between the rivers. The internal drainage was designed to be organized by levels or districts each of which includes the fen parts of one or several parishes. The details of the organization vary with the history of their development but the areas include: