New route for predatory fish to save drinking water in Hornsjön on Öland

According to Viktoria Nilsson, who is an environmental engineer at Borgholm Municipality, the water quality in Hornsjön is currently poor.

This can be seen, among other things, through poor depth of view and cloudiness.

- The fact that the water quality in Hornsjön is poor has to do with, among other things, leakage from agriculture and dug up dry land in Uppströmsjön.

But it also has to do with the fact that fish have not been able to come up to the extent that is really needed, says Viktoria Nilsson who is an environmental engineer at Borgholm municipality.

Migration barriers for fish

When Borgholm energi applied for permission from the Land and Environmental Court in 2019 for continued regulation of Hornsjön, they also applied for permission to build a fish passage at the lake's outlet.

This is because the dam that regulates the lake has so far constituted a migration obstacle for fish and other aquatic organisms, something that has upset the ecosystem.

- It means that predatory fish eat smaller fish that eat zooplankton.

Zooplankton, in turn, are the ones that eat algae, and if there aren't enough zooplankton that eat algae, then you upset the system, says Viktoria Nilsson.