Before drainage, the fens contained many shallow lakes, of which Whittlesey Mere was one of the largest. The River Nene originally flowed through this mere, then south to Ugg Mere, before turning east towards the Ouse. By 1851, silting and peat expansion had reduced Whittlesey Mere to about and only a metre deep. In that year the mere disappeared, when new drains carried waters to a pumping station and up into Bevill's Leam. The drainage turned both the mere and the Holme Fen into usable farmland, but subsidence followed.