Water company, United Utilities, has been fined £8,000 for polluting a river in Blackburn.
They were prosecuted follwing a 2,700-litres diesel spill last year at Fishmoor water treatment works.
Environment Agency visited the site in January 2010 and found pollution to a 1km stretch of Higher Croft Brook near the River Darwen.
Diesel fuel was entering the brook as a result of an incident at the site when a generator had been overfilled and a safety valve failed to close.
It was found that a plug was missing from the generator and if it had been in place the leaked diesel would have been contained.
The water company pleaded guilty at Hyndburn Magistrates Court and was ordered to pay costs of £3,048.
