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Researchers analysed brown trout at 71 sites in Britain and Ireland, where many rivers contain metal washed out from disused mines.

I watch a brown trout mistake the flitting shadow of a dragonfly for the thing itself and dart to the surface.

There were also "quite a few" larger dead specimens including chub, barbel and brown trout that had been seen.

The river is used for breeding Atlantic salmon and is home to native wild brown trout and smaller species like bullheads and loaches.

Natural river features such as riffles - shallower, faster moving sections of a stream - have been restored to attract white-clawed crayfish and brown trout.