the landscape to the east and west of the river is also remarkable. peat extraction in the 17th and 18th century turned vast low-lying fens into a collection of shallow, man-made lakes and bogs. water lilies, reeds, swamps and wooded areas have developed spontaneously from the old peat canals ("trekgaten") where the peat was extracted. a total of about 70 square kilometres have been designated as a series of nature reserves and are part of the european natura 2000 scheme.