The water level is crucial for the wading birds' food supply
The water level affects the feeding areas of the birds. At high water, there will be fewer open mud surfaces, and the aquatic plants may be too deep for geese and ducks. Numbers of waterfowl from Nordre Øyeren Bird Station show that the height of the water level is related to the number of waterfowl that choose to stay in the area. If the water level is too high, many of the birds will move away and search for food elsewhere. See graph to the right.
In 1862, Øyeren was dammed up at Mørkfoss and the water level in Øyeren is today regulated. The water level is kept higher for large parts of the year, compared to what it would have been naturally. This leads to reduced food supply for the waterfowl.