Europe's ongoing heat wave has claimed the lives of thousands of fish on the German-Swiss border.

Iran press/ Europe: Authorities retrieved over a ton of dead fish from the upper Rhine River over the weekend, the Swiss Fishery Association confirmed on Monday.

Most of the fish were graylings, which thrive in 23 degree water. The heat wave caused the water to rise to 27 degrees in which the fish could not survive.

Switzerland's fishery association had tried to prevent the deaths by creating six pools of cooler water. Fish had taken shelter there last week, but the measures were insufficient to keep them alive.