Severn Trent Water Ltd has been fined £24,000 after polluting Heapham fishing lake in Gainsborough for the fourth time in seven years. Hundreds of fish died in April 2011 when a blockage in the foul sewer was not cleared for more than a week because of an IT and scheduling errors Lincoln Magistrates’ Court heard today (Tues).

Mrs Claire Corfield, prosecuting for the Environment Agency, said sewage and trade effluent had polluted a stream that passes through Heapham Lakes, owned by West Lindsey District Council as part of a flood protection scheme. The pollution continued into the River Till and more than three miles of water had been affected. The company was also ordered to pay full costs of £6,884. Severn Trent was alerted by the council to sewage flooding at Theaker Avenue Nature Reserve on 29 March.

On 8 April the Environment Agency was contacted by the council’s angling club which reported dead fish in the lakes. A sample taken from the lake showed grossly polluting levels of BOD (Biochemical Oxygen Demand) 172 times higher than would be expected in unpolluted water and gasping fish had to be rescued.

On 8 April, 360 dead fish were counted floating on the surface including carp, bream, tench and pike. Heapham Lakes is used by anglers but, the court was told, it was the third time that sewage pollution caused by the water company had stopped fishing there.

In April 2004, 7,000 fish were killed and four months later, fish used to restock were also killed by pollution.

Three years later there was a further pollution. A service delivery manager for Severn Trent, told investigating officers that just before the incident they had moved to a new method of working. They discovered a compatability problem with a new IT system used for prioritizing work which led to jobs being moved to an error queue and the incident not being attended to for two days. There were also scheduling errors which meant that the blockage in the south sewer was not cleared until 7 April.

A report of sewage flooding would normally be responded to in six hours. He said it was believed the blockage at the back of Dove Close was caused by a discharge of fats combined with rags. The sewage flooded land at the nature reserve, entered a defective private surface water chamber linked to the network and was carried to the stream via the surface water outfall at White’s Wood Lane. Since the pollution the company has made changes to its IT system, the affected stretch of sewer will now be cleaned twice a year, the outfall is being regularly checked, the private surface water chamber has been sealed and early warning systems in manholes are being installed. He said the company had spent £84,000 on investigating the incident and remediation.

The company said it would pay for the restocking of the lake. After the hearing Environment Agency officer Sarah Gillanders said: “An extensive clean-up operation was needed after this pollution and fish had to be rescued from the lake and moved to safety. “Had Severn Trent responded sooner, the serious effect of the pollution could have been minimized.”

The angling club has stopped charging subsidies to its members as a result the previous incident. Mark Scoggins, for the company, said this was not a case of ignoring a problem A crew went to the nature reserve three times to try to clear the blockage. Had the company known that there had been a pollution they would have responded quicker.

Severn Trent Water pleaded guilty to: On or about 8 April 2011, you did cause poisonous, noxious or polluting matter, namely sewage and trade effluent to enter inland freshwaters, namely a tributary of the River Till at Gainsborough in the County of Lincolnshire Contrary to Regulation 12(1)(b) and regulation 38(1)(a) of the Environmental Permitting (England and Wales) Regulations 2010