United Utilities has been fined £10,000 for discharging sewage into a brook and ordered to pay costs of almost £3,000.
The company pleaded guilty to the offence, which occurred in September 2007. The pollution was the result of a pump failure at Hindley pumping station at Hindley, near Wigan.
The court heard that the Environment Agency were contacted by a member of the public who reported that Hey Brook had turned grey in colour and was teeming with dead and dying fish. There was also a smell of sewage in the area.
A pump failure at Hindley pumping station caused sewage to flow into storm overflow tanks, instead of being pumped to the sewage treatment works, as would normally happen. As the volume in the tanks increased, sewage overflowed into neighbouring Hey Brook.
More than 5,000m3 of sewage was discharged into Hey Brook, affecting approximately 6km of the brook from Hindley pumping station to Pennington Flash - a local lake and nature reserve.
There may have been some localised effect on Pennington Flash, but it is likely that the size of the lake would have acted to dilute the effluent and minimise any impact.
Investigations carried out by Environment Agency officers indicated that the pollution had a significant impact on the ecology of Hey Brook and that more than 100 fish were killed.