Lake Öljaren in Södermanland has been experiencing major problems with eutrophication and algal blooms for a long time. There is hardly any life at all at the bottom of the lake. Eutrophication is caused by old nutrients being released from the bottom of the lake – this is known as internal loading.
The municipality of Katrineholm has tried low-flow dredging as a way of helping the lake. The top layers of bottom sediment are sucked up using hoses operated from a pontoon on the lake and cleaned in several stages on land. The nutrient-rich sediment that remains can be used as fertiliser on arable land, thereby returning to a positive cycle. The purified water is pumped to a ditch that flows back into Lake Öljaren.
It is hoped that Lake Öljaren will regain its natural equilibrium, with clear water and rich plant and animal life in the water.
