THOUSANDS of fish have been poured into the River Colne – to give stocks a welcome boost.

Environment Agency staff added 4,000 grayling across four sites yesterday to help return the once-contaminated river to its former fishing glory.

It comes after fish stocks were hit two years ago following a pollution incident, which damaged fish populations.

A huge blaze at Grosvenor Chemical plant, Linthwaite, in 2010, caused contaminated water to pour into the River Colne during the course of the firefighting operation.

To help with the recovery, fisheries officers released 1,000 fish at four locations between Marsden and Milnsbridge.

Peter Mischenko, fisheries technical officer at the Environment Agency, said: “Grayling are an important species in a watercourse.

“They require water with a high oxygen content, and so their presence is usually a sign of good water quality.

“Anglers have come from as far afield as Holland to fish for them in the River Colne.

“This stocking should help to boost numbers in the river as part of an exercise that was started the year after the pollution incident.”

The young grayling are nearly five months old and have been bred and grown at the agency’s fish farm at Calverton in Nottinghamshire, in a specially designed system that ensures they can thrive in the River Colne.

It is expected they will continue to grow in the river and some of them will begin to spawn in the spring of 2014.

It is hoped that by stocking these young fish over the next few years, the population of grayling in the river will return to healthy numbers.

Peter added: “Nature will take care of it itself. This is just offering a helping hand to help it along.”