AN INVESTIGATION is under way to find out why 170 fish were found washed up on the banks of the River Wear last week.

One possibility is that chlorine escaped from a new water treatment plant in upper Weardale and contaminated the river, poisoning the fish.

Northumbrian Water's Wear Valley Water Treatment Works, at Wearhead, is suspected to be the source of the leak and is being investigated.

The £28m development, which is now being commissioned and is expected to be operational by the end of the year, replaces two sites at Wearhead and Tunstall Reservoir.

The Environment Agency confirmed that there was an incident which led to the death of fish in the river but said it was too early to say whether it will consider legal action.

Local environmentalists are calling for urgent answers about how the disaster occurred and say it must be prevented from happening again.

Peter Stephenson, secretary of the Weardale Environmental Trust, said: "This is dreadful news. Weardale is a beautiful area and very special wildlife habitat.

"The River Wear is an important sea trout spawning area, and brown trout habitat so accidents like this cannot be allowed to happen."

Due to the nature of the area, which is regarded as an Area of Outstanding Natural Beauty, the company had to go through a consultation process, involving meetings with a variety of agencies before gaining permission to build the works.

These included talks with Wear Valley District Council, Durham County Council, the Countryside Agency, English Nature, The Environment Agency, and a number of local interest groups.

Along with designing the plant in keeping with the local landscape, the company pledged to contribute to the local environment and promote wildlife habitat by replacing the old works with a wetland nature reserve.

It is hoped this will protect wildlife, especially the local population of endangered water voles, currently found at Burnhope Burn.

But Mr Stephenson said the Weardale Environmental Trust was not satisfied that all its concerns about the impact of the works on the area had been addressed and called for tighter monitoring of the site.

A spokesman from Northumbrian Water said: "We are aware that there was an incident and are assisting the Environment Agency fully with its inquiries."