WESSEX Water has been prosecuted and fined £6,000 for accidentally releasing poor quality sewage into the Bickerley Millstream in Ringwood.

Wessex Water Services Ltd of Bath pleaded guilty at New Forest magistrates to a breach of discharge consent at its Ringwood Sewage Treatment Works, which caused the waste to flow into the tributary of the river Avon.

The Avon is designated as a Special Area of Conservation and is an important spawning base for Atlantic salmon.

A call was received by the Environment Agency on September 23 from a member of the local angling club saying that the Bickerley Millstream below the sewage treatment works discharge point was discoloured and had an unpleasant odour, the court heard.

An environmental officer attended the sewage treatment works and found thick brown liquid flowing out of the gateway and into the road.

Further investigation found a valve on a sludge tank had been left open after routine maintenance leading to effluent flowing from the primary tank into the sludge storage tank, which then overfilled.

An ultrasonic level detector on the sludge storage tank, which would have raised the alarm to the pollution, was monitoring an empty tank that was not being used rather than the overflowing one, the court heard.

Wessex Water is permitted to discharge only treated effluent of a certain quality into the millstream.

"The Hampshire Avon is a high quality river suitable for salmon and sea trout," said Emma Tattersall, from the Environment Agency.

"Both of these species of fish are vulnerable to pollution.

"Sewage treatment works have the potential to pollute, so it is important water companies operate in such a way as to ensure these works fully comply with the conditions of their discharge consents."

In addition to the fine, the water company was also ordered to pay £978 costs.

"The incident was caused by operator error and subsequently we have changed a number of things," said a spokesman from the company.

"We have installed an alarm warning system, retrained the site staff and issued a new work checklist, to make sure this problem does not happen again."