WATER company United Utilities has paid out more than half-a-million pounds after chemical leak killed a "significant" number of fish in the River Douglas at Horwich.

Brown trout perished after a spill of acidic ferric salt solution from the Rivington Water Treatment Works turned the river ­— which flows out of Rivington reservoir ­— orange and made it "very acidic".

The environment Agency investigated the incident in September 2016 and it was found that the ferric solution had been by-passing a faulty valve in the water treatment works, which had discharged into a drain and entered the river.

United Utilities, which admitted the offence, has taken action to prevent the pollution as well as a payment of £500,000 to the Douglas Catchment Partnership, led by the environmental charity Groundworks, for the building of fish passages or bypass streams, within the River Douglas catchment and further pro bono support to the project, which will directly benefit the local environment.

United Utilities has also spent £88,498 on actions to prevent a recurrence of the incident and paid £13,521 in Environment Agency costs.

Jennifer Hall, at the Environment Agency, said: "We take tough action against any company or individual who causes significant pollution and damage to the environment.

“We urge anyone who notices pollution to land or water to call our 24 hour free hotline on 0800 80 70 60. Over the course of the past year the number of serious and significant pollution incidents reduced to their lowest levels since 2011 but there are still far too many serious pollution incidents which damage the local environment, threaten wildlife and, in the worst cases, put the public at risk.”

Sara Clowes, from Groundwork, said: “The River Douglas Catchment Partnership are working collaboratively with a core group of dedicated environmental organisations and local landowners to develop a robust long term fisheries strategy to improve fish passage, wildlife habitat and raise public awareness about how we can all play a role in safeguarding the health of our waterways into the future.”

Polluters can make an offer to the Environment Agency to pay for or carry out environmental improvements as an alternative to any other enforcement action and the Environment Agency decides whether this is acceptable. Enforcement Undertakings differ to cases which are dealt with in court, as they result in money being spent directly protecting, restoring and improving the environment.

A United Utilities spokesperson said: “We apologise for the pollution incident that affected the River Douglas in September 2016. At the time, we fully cooperated with the Environment Agency’s investigation, and took the necessary action to prevent a reoccurrence.

“We also funded several projects carried out by charities and other organisations that directly benefitted the environment within the River Douglas catchment area.”

Incidents can be reported to the agency 24/7 on 0800 807060.