Last summer, dozens of dead roaches were found in Mustajoki. The reason for the pollution of the river is not yet known.
The Southeast Finland ELY Center investigates fish deaths in Lappeenranta’s Mustajoki. The Ely center received the first information about the fish deaths in Mustajoki last Midsummer.
The water samples taken by the ELY center revealed that the oxygen concentrations in Mustajoki are remarkably low. In addition, very high concentrations of ammonium nitrogen were found in the river. Both concentrations are harmful to fish.
The cause of the contamination is unknown
The cause of Mustajoki’s pollution is not yet known. One of the more common reasons for ammonium nitrogen entering the water is the runoff of sludge manure into the river during heavy rains.
The dead roaches found in the river last year were not the only victims of the deterioration of Mustajoki’s water quality.
– If more roach have died, then it can also be assumed that other fish have also died, Vaitinen says.
A setback to the original sea trout population
Mustajoki’s high ammonium nitrogen concentrations and low oxygen concentrations also affect the river’s significant trout population. Last September, not a single trout born in the same spring was detected in the main bed of the Mustajoki during electrofishing. In previous years, similar trout have appeared by the dozens.
Mustajoki is an important river in Southeastern Finland because of its trout. Mustajoki is the only river in Southeast Finland where the original sea trout population still exists. The trout population of Mustajoki is used to restore and revitalize the trout populations of other rivers leading to the sea. In Mustajoki, among other things, a lot of rapid renovations have been done to support sea trout.
– Other than that, Mustajoki has been doing very well. This has been quite a setback for the development that has been achieved there with the renovations, Vaitinen says.