Great Level

The Fens
Natural region
The Fens from Sheepwash Crossing
Map of eastern England, showing position of the Fens.
Countries	Eastern England

The Fens, also known as the Fenland(s), is a naturally marshy region in eastern England. Most of the fens were drained several centuries ago, resulting in a flat, dry, low-lying agricultural region. It is one of the driest areas in England, thanks to a system of drainage channels and man-made rivers (dykes and drains) and automated pumping stations. A common misconception is that the fens are damp.

A fen is the local name for an individual area of marshland or former marshland and also designates the type of marsh typical of the area, which has neutral or alkaline water chemistry and relatively large quantities of dissolved minerals, but few other plant nutrients.

Fenland primarily lies around the coast of the Wash; it reaches into four ceremonial counties: Lincolnshire, Cambridgeshire, Norfolk and a small area of Suffolk, as well as the historic county of Huntingdonshire. In whole it occupies an area of nearly 1,500 sq mi (3,900 km²).

Most of the Fenland lies within a few metres of sea level. As with similar areas in the Netherlands, much of the Fenland originally consisted of fresh- or salt-water wetlands, which have been artificially drained and continue to be protected from floods by drainage banks and pumps. With the support of this drainage system, the Fenland has become a major arable agricultural region in Britain for grains and vegetables. The Fens are particularly fertile, containing around half of the grade 1 agricultural land in England.

The Fens have been referred to as the "Holy Land of the English" because of the former monasteries, now churches and cathedrals, of Crowland, Ely, Peterborough, Ramsey and Thorney. Other significant settlements in the Fens include Boston, Cambridge, Spalding, and Wisbech.