Fish die in chemical pollution incident in River Colne in Huddersfield as Environment Agency launch investigation

Members of the public reported seeing the dead and distressed fish in the water at Aspley, near Huddersfield.

The substance involved has been identified as sodium hydrocholrite - a disinfectant and bleaching agent - but it is not known where the chemical came from or who is responsible for its illegal release into the river.

The Environment Agency said: "We received reports of dead and distressed fish in the River Colne on September 2 and responded immediately. Our incident response officer attended the site and found that the water had been polluted with sodium hypochlorite, killing a number of fish and other aquatic life. Our investigation has confirmed the sodium hypochlorite has stopped flowing into the water. We’re now investigating the circumstances that led to the pollution."

The river flows from west to east through the Colne Valley passing through Marsden, Slaithwaite and Milnsbridge to Huddersfield and then on to Cooper Bridge where it joins the River Calder.

Its soft acidic waters, which flows down into the valley from the peat moorlands above, played a role in the valley's history of wool production, as it was believed to help produce fine quality fabric from the local mills.

Nowadays, factories and other industrial plants along the river must meet rigorous Environment Agency regulations to prevent harmful discharges into the water.

Waste which inadvertently found its way into the Colne following a chemical factory fire in 2010 caused the deaths of large numbers of fish in the river and the nearby Huddersfield Narrow Canal.