These two links to sites describing the Fens in the industrial age:
Prickwillow Drainage Engine Museum
(former Prickwillow Drainage Engine Museum site)
Unfortunately the link which showed the extent of the Fens, stretching
North to The Wash from Cambridge, is no longer there to refer to.
However, the Prickwillow Drainage Engine Museum site has good
information on the hitory and extent of the Fens.