Yorkshire Water has been fined £6,000 after it pleaded guilty to polluting a beck.

The company, which has its headquarters in Halifax Road, Bradford, was also ordered to pay full costs of £1,827 to the Environment Agency, which brought the case.

Ben Reid, prosecuting for the Environment Agency, told Calderdale Magistrates' Court in Halifax that a combined sewer overflow (CSO) at Wyke Old Lane, Brighouse, had blocked a number of times in recent years and had repeatedly sent sewerage into Clifton Beck, having a serious impact on its aquatic life.

The CSO blocked on May 2003, October 2003, November 2004 and September 2005. Yorkshire Water was cautioned and fined in 2003 after the blockages caused sewerage to enter the beck.

Mr Reid told the court it took the company until 2006 to install a warning system. Even after the warning system was installed, the CSO again blocked and sent sewerage into Clifton Beck.

A biological survey found that the pollution was chronic and had a significant impact on aquatic life. It was estimated that a pollution outbreak last June killed 33 per cent of the animal life assessed.

Mr Reid said a telemetry system at the site had failed, so Yorkshire Water was not notified when there was a problem with the CSO. It appeared that the system had stopped working in April last year, unbeknown to the company.

However, a sensor was still working, and data from this showed tha during April 20, 2006, to June 20, 2006, the CSO sent nine illegal discharges into Clifton Beck.

In mitigation, Yorkshire Water Services Ltd said that the blockage was caused by an object put in the system by a third party.

Speaking after the case, an Environment Agency spokesman said: "This case had a significant impact on aquatic life in Clifton Beck. Yorkshire Water has a duty to maintain its monitoring equipment and we will prosecute any company that fails to take its responsibility seriously."