Pulse trawling in Lake Hjälmaren (night-time)

Det är natt och strålkastare lyser upp en båt i ett vatten omgivet med hög vass. Två personer står i båten med håvar i händerna. Skenet gör att båten ser röd ut. Vattnet är ljusgrönt och vassen turkos. Omgivningen är helt svart.

Some fish can actually increase eutrophication of a lake. Living organisms in the lake interact with one another and influence the aquatic environment. White fish such as roach and bream eat a lot of zooplankton. A decrease in zooplankton results in more phytoplankton, which cause algal blooms. Bream also root around in the lake bed, and this can release nutrients into the water.

Reduction fishing – catching large quantities of white fish – is a tried and tested way of tackling eutrophication and creating a more sustainable balance between zooplankton and phytoplankton. The phosphorus in the fish themselves is also removed from the lake. Less phytoplankton in the water also results in better visibility. This improves hunting opportunities for perch and pike and restores the natural ecosystem.