The Environment Agency (E.A.) has released 5000 young Grayling (Thymallus thymallus) into part of the River Colne in West Yorkshire, near Huddersfield.
The river's population of the fish was severely damaged last year after a pollution incident following a factory fire when chemicals and glue seeped into the river, poisoning fish.
The E.A. raised the fry at its fish farm in Calverton, Nottinghamshire from eggs stripped from adults caught in the nearby River Nidd in North Yorkshire.
It is hoped the fish will thrive and spawn themselves once mature in two years' time, helping to make the area a popular attraction to fishermen and wildlife once more.
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