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Thousands of fish have died in Swiss sections of the River Rhine as Europe's heatwave continues.

Swiss authorities say they have pulled a tonne of dead fish from the river and have tried to implement emergency measures to save others.

The rising heat has lowered oxygen levels in the water, making it hard for fish to survive.

Europe is experiencing a prolonged heatwave that has caused wildfires as far north as the Arctic Circle.

The fish most affected is the grayling, which fares better in cooler waters and starts to struggle when the temperatures rises to about 23C (73F).

But temperatures on the Swiss section of the Rhine have risen to more than 25C (77F), and combined with falling water levels it has caused the deaths of thousands of fish.

Fishery authorities in three Swiss cantons along the river set up cool water pools where the animals could find some respite.

But despite their efforts they have collected a tonne of dead fish so far - between a quarter and a third of the yearly catch.

In 2003 about 50,000 grayling died in the Rhine in Switzerland when water temperatures rose to up to 26C (79F).

Fish have also been dying in the northern German city of Hamburg, where temperatures in the Alster river - a tributary of the Elbe - reportedly rose to 27C (81F).

And in the UK, the Environment Agency said 6,000 fish died in Essex, Norfolk and Suffolk during the recent heatwave.