The fish mortality is due to a critical lack of oxygen in the water, which was exacerbated by the persistently low water level. The lake is normally fed by the Glattbach, also known as the Brünnlesbach. However, this has dried up completely and can no longer supply the Fleischlesee with fresh water. As a result, the body of water has "tipped over".
The local fishing association will salvage the dead fish - as far as possible - to prevent further pollution of the water.
The Fleischlesee is not a designated bathing water. There is therefore no health risk for people.