the fens

The Cambridgeshire Fens covers an area of about 200 square miles of very flat land, between the cities of Peterborough and Cambridge.
The land was originally very marshy with just a few areas of more solid ground where settlements were built. The suffix -ea- means island and consequently many of the place names end in 'ea' or 'ey' : Ely, Whittlesey, Manea, Thorney.
In the 17th century, the Fens began to be drained and much of the area today is still criss-crossed by a network of man-made rivers and dykes.

The history of the Fens is fascinating and if you would like to read more the website of  the Great Fen Project is a very good place to start.