The cows liked to slake their thirst by drinking from a stream feeding Ingbirchworth Reservoir, left, between Huddersfield and Sheffield.

But their hooves were stirring up the stream bed and muddying the water, making it less attractive to brown trout on their way to spawn.

Working together with tenant farmers, Yorkshire Water and the Environment Agency installed a drinking trough for the cattle, fed from the stream, and then constructed a fence to give the narrow watercourse the chance to recover.

A fish pass has been installed to make the journey upstream easier and brown trout have now started to appear in what looks set to become a new spawning ground.

"It's great to have a real success story to tell," said Yorkshire Water's environmental assessment manager, Mark Tinsdeall.

Water quality had been improved and biodiversity enhanced, he said, while farmers were happy they had a reliable supply of water for their cattle.