THE Environment Agency is continuing investigations after an acid substance polluted a Chorley river killing 5,000 fish.

Fisheries officers are gathering evidence after 300 litres of a mix of hydrocholic and nitric acid was released into the River Yarrow killing every single fish within a five mile stretch.

Agency officials say they have identified the source -- believed to be an industrial premises -- but are not releasing names.

The stretch of water was polluted to such an extent that its Ph reading was 'two' - the highest acidic reading possible is 'one'.

Brian Shields, Environment Agency fisheries officer, said: "The water quality was improving steadily over the last few years by working in partnership with industrial premises in the area and stocks were increasing.

"Now with the breeding season just beginning it has happened at a bad time."

Breeds of fish killed include chub, roach, perch, brown trout and pike. There have even been salmon spotted in the river in the last six months and it is feared they could have been poisoned too.

The majority of the insect population was also wiped out.

Mr Shields said: "Businesses are allowed to discharge chemicals into the river within set guidelines and under licence so that a good quality of water is maintained.

"But this was just such a toxic fluid."

The Environment Agency said it was grateful to the member of the public who alerted them within hours of the pollution occurring. Mr Shields said: "They were walking along the river in Euxton and noticed a large number of dead fish.

"This enabled us to get out quickly and identify the source. We depend a lot on members of the public."

The Environment Agency is advising people to stay clear of the affected stretch until further notice.