Two rivers could be permanently damaged and an endangered species of crayfish threatened if the Western Link is built, a conservation charity has warned.

Eastern Daily Press: David Diggens, chief executive of the Norfolk Rivers Trust. Picture: Ian BurtDavid Diggens, chief executive of the Norfolk Rivers Trust. Picture: Ian Burt (Image: Archant © 2013)

The Norfolk Rivers Trust has joined Norfolk Wildlife Trust in opposing the controversial £153m road, which would connect the Norwich Northern Distributor Road to the A47.

The rivers trust said the road, which would travel between Weston Longville and Ringland, including a 720-metre-long viaduct, is likely to cause permanent damage to the rivers Wensum and Tud.

Chief executive David Diggins said those rivers are globally rare and increasingly threatened habitats, with the Wensum designated as a Special Area of Conservation.

He said: “The development would result in the destruction of globally and nationally important ecological water features, for which mitigation and compensation are not feasible.”

Eastern Daily Press: The route of the proposed Western Link. Pic: Norfolk County Council.The route of the proposed Western Link. Pic: Norfolk County Council. (Image: Norfolk County Council)

He said the road could threaten the white-clawed crayfish - the UK’s only native freshwater crayfish - which are protected by law. They are in the Tud, and thought to be in the Wensum.

Mr Diggins said: “The development would negatively impact one of only four known remaining populations of white-clawed crayfish in Norfolk, listed as endangered on the IUCN (International Union for Conservation of Nature) Red List.

“They have very specific habitat requirements and the crayfish and their habitats are threatened by abstraction, pollution, habitat destruction, invasive species and the impacts of road and housing development generally.”

Mr Diggins said the development would also, potentially, lead to the loss of a breeding colony of endangered barbastelle bats.

Eastern Daily Press: Martin Wilby, Norfolk County Council cabinet member for highways, infrastructure and transport.Martin Wilby, Norfolk County Council cabinet member for highways, infrastructure and transport. (Image: Archant)

He said it would “negatively impact” other protected species such as otters, water voles, lamprey and eels, due to the increased disturbance from extra traffic, light pollution and run-off.

Martin Wilby, Norfolk County Council’s cabinet member for highways and infrastructure said: “From the outset, we have stated that the Norwich Western Link will be designed to not affect the integrity of the River Wensum Special Area of Conservation.

“This can be achieved through the design of the viaduct on which the road would cross the river and its flood plain, as well as through the construction methods used.

“A viaduct crossing of the river was chosen instead of a lower level bridge to prevent and mitigate against many of the potential effects the Norfolk Rivers Trust have raised, and we have regularly sought advice from Natural England and the Environment Agency on our proposals.

“The Norwich Western Link will not cross the River Tud, which was a factor that was considered when deciding on a route for the road.” Mr Wilby said there was still a “significant” amount of work to do to finalise the details of the scheme and mitigation measures, so he hoped the rivers trust would review its position in the future.

What are white-clawed crayfish?

The white-clawed crayfish is the largest native freshwater crustacean species.

Once widespread in Europe, it is being severely affected by the non-native signal crayfish, which were introduced for farming and aquaculture in the 1980s, but ended up in water courses.

The signal crayfish are twice as big as the white-clawed crayfish, which tend to only be about 6cm to 12cm long, and are highly aggressive. That means they out-compete the smaller, native, species for food.

The white-clawed crayfish have pinkish-white claws and a pitted appearance ranging in colour from brown to olive. They are predominantly nocturnal and hide in crevices or under stones.

They are protected by the Wildlife and Countryside Act and the Countryside Rights of Way Act.

The white-clawed crayfish, which has a lifespan of eight to 12 years, is listed as Endangered on the global IUCN Red List of Threatened Species.