River Wandle oil spill has 'undone decades of work' to return wildlife to London river, MP warns

An estimated 4,000 litres of oil spilled into the River Wandle - (Supplied)

Thousands of litres of oil which polluted a rare chalk stream in south London has undone “decades” of environmental work, an MP has said.

An estimated 4,000 litres of oil spilled into the River Wandle on Tuesday, home to wildlife such as brown trout and kingfishers.

The impact of the “environmental disaster” will be measured in years, warned Carshalton and Wallington MP Bobby Dean, as he called on Environment Secretary Steve Reed to visit the site.

(Supplied)

The spill, thought to have come from a storage tank at a nearby bus depot, could continue to wreak havoc on wildlife for a long time to come, the Liberal Democrat told Mr Reed in a letter.

He said: “This spill has undone decades of work by hundreds of volunteers who have helped restore the Wandle from an ecologically dead river to a thriving ecosystem.

“While we await the findings of the Environment Agency’s investigation, one thing is clear: this should never have happened. Those responsible must pay.”

Mr Dean hit out at ministers for not yet making a statement on the incident, which came days after the Environment Secretary pledged in an interview to “streamline” environmental regulations which act as a “blocker to growth”.

The Wandle flows through south London (Alamy/PA)

An Environment Agency spokesperson said it “immediately” deployed officers to limit damage to wildlife, and had taken measures to stop the leak.

The spokesperson added: "We are currently gathering evidence and assessing the environmental impact for our investigation, with the pollution source suspected to be a bus depot storage tank in Thornton Heath, Croydon."

The Wandle, which flows for nine miles from its source to the Thames, became heavily industrialised from the 17th to 19th centuries, suffering from severe pollution.

For many years the waterway was considered "ecologically dead", according to the South East Rivers Trust, but there has been a considerable effort to clean up the river and it is now a popular walking trail.

It is home to brown trout, a key chalk stream species, which was re-introduced to the river, while the Wandle and surrounding habitats support wildlife including kingfishers, damselflies and bats.

Chalk streams are a globally rare habitat, most of which are in England, and face a range of threats including climate change, over abstraction of water and pollution from sources including farming, urban run-off and sewage.

The National Trust, which looks after nearby Morden Hall Park and Watermeads nature reserve said it was aware of a "significant diesel spill" that had entered the Wandle upstream from the park, which the river then flows through.

A spokesperson said: "Our waterways and wetlands are precious environments, and any pollution incident can greatly affect our wildlife.

"Our teams are working closely with the Environment Agency to help ensure the site can recover as quickly as possible.”