thumb|right|Prickwillow Museum shows the changing face of the Fens and the story of their drainage. It is housed in an old pumping station. The dead vegetation of the peat remained undecayed because it was deprived of air (the peat being anaerobic). When it was drained, the oxygen of the air reached it, since then the peat has been slowly oxidizing. This, together with the shrinkage on its initial drying and the removal of soil by the wind, has meant that much of the Fens lies below high tide level. As the highest parts of the drained fen are now only a few metres above mean sea level, only sizeable embankments of the rivers, and general flood defences, stop the land from being inundated. Nonetheless, these works are now much more effective than they were.
thumb|right|Prickwillow Museum shows the changing face of the Fens and the story of their drainage. It is housed in an old pumping station. The dead vegetation of the peat remained undecayed because it was deprive.d of air (the peat being anaerobic). When it was drained, the oxygen of the air reached it, since then the peat has been slowly oxidizing. This, together with the shrinkage on its initial drying and the removal of soil by the wind, has meant that much of the Fens lies below high tide level. As the highest parts of the drained fen are now only a few metres above mean sea level, only sizeable embankments of the rivers, and general flood defences, stop the land from being inundated. Nonetheless, these works are now much more effective than they were