THAMES Water has been ordered to pay £58,000 in fines and costs after raw sewage spilled out of one of its water treatment plants.

More than 8,000 fish, including 83 rare brown trout, were killed when the effluent poured into the River Ray.

About five miles of the river, a tributary of the Thames, were affected from south of Broome Manor to Moredon Bridge.

The toxic waste flooded footpaths, flowed through a forest and onto playing fields after the storage tank on Pipers Way, Old Town, overflowed.

The unmanned Broome station normally only stores water and sewage during storms to stop drains in the town backing up.

But on June 15, 2003, a blockage meant that for 12 hours raw sewage flooded into woodland across the road.

Swindon Crown Court heard that the problem probably started at about midday when an alarm at the station activated saying it was about to overflow. However within six minutes a short circuit meant it reset itself, and Thames Water workers in the control centre in Rickmansworth, Herts, did not realise anything was wrong.

Three hours later a member of the public reported a leaking manhole cover and by 4.30pm the problem was identified.

But Thames Water failed to tell the Environment Agency and it was only alerted by a jogger who came to a sewage flooded footpath.

Prosecutor Richard Banwell said an officer found ammonia in the river five times the danger level and oxygen greatly depleted.

8,025 fish perished as a result including 83 brown trout, some up to 40cm long. Other creatures and organisms, including freshwater shrimps, were also killed off. Mr Banwell said that Thames Water then refused to co-operate with an investigation into the incident and that in the last year the company had been convicted of 10 similar matters.

Ben Fitzgerald, defending, said the flooding was out of Thames Water's control and blamed a piece of wood trapped in the pipe.

He said the alarm at Broome was checked monthly and was last inspected less than two weeks before it failed. Once the blockage was identified he said they did everything possible to clear it.

He said that the company, which admitted one count of discharging effluent, took environmental issues seriously.

Fining them £50,000 with £8,270 costs, Recorder Michael Tennant said: "The defendant's response appeared to suggest they were cavalier in their approach.

"The time taken to solve this problem was far too long given the amount of damage which was likely to result and did result."

Thames Water's Tom Kelly said an appeal is being considered.

Jamie Hill