United Utilities has been fined £14,000 after 10,000 cubic metres of sewage was discharged into the river Lune at Lancaster.
The Environment Agency successfully secured a prosecution at Lancaster Magistrates Court on Friday December 14.
United Utilities pleaded guilty to causing an unauthorised water discharge activity and failing to comply with a condition of its environmental permit at its Willow Lane Pumping Station.
The company was also ordered to pay costs of £2,423.79.
The court heard that on or about August 20 2011 at Willow Lane Pumping Station United Utilities estimated that over 10,000 cubic metres of sewage was discharged into the River Lune at an environmentally sensitive location and the discharge continued for more than 37 hours.
The failure to replace a standby pump and the failure of an alarm system to activate were found to have contributed to this incident.
The discharge occurred 1.5km upstream from the Lune Estuary, which is a designated Site of Special Scientific Interest, a Special Protection Area, a Special Area of Conservation and RAMSAR site.
Investigation by the Environment Agency found the discharge would have impacted on nearby bathing waters and shellfish waters.
There was also the potential for harm to recreational users of water, including bathers, as the discharge continued in dry weather.
In mitigation, the court heard that United Utilities had reported the incident to the Environment Agency and co-operated throughout the investigation.
Sean Wannop of the Environment Agency, said the incident may have been avoided if United Utilities had acted sooner in replacing the damaged standby pump.
A spokesman for United Utilities said: “We take our environmental responsibilities very seriously and do our best to improve the environment, not pollute it.
“The court took into account the fact that over the last eighteen months we have been assisting the Environment Agency voluntarily by providing temporary pumping at a private pumping station with a history of spills downstream of Willow Lane.
“We have now put robust measures in place to make sure there cannot be a recurrence of the problems at Willow Lane pumping station.”