River Wandle clean-up after diesel spill

Some 4,000 litres of oil spilled into surface water drains, affecting the River Wandle

The clean-up is still under way after a diesel spill polluted a chalk stream in south-west London on Tuesday.

The Environment Agency said an estimated 4,000 litres of oil spilled into surface water drains and affected the River Wandle, a once-heavily industrialised chalk stream that had been revived and is now home to wildlife such as brown trout and kingfishers.

It is expected the spill, thought to have come from a storage tank at a nearby bus depot, will affect the Wandle from Beddington to Wandsworth over the coming days.

The Environment Agency spokesperson added: "We are currently gathering evidence and assessing the environmental impact for our investigation."

Wildlife has been left covered in oil

The Liberal Democrat MP for Carshalton and Wallington, Bobby Dean, said: "It's nothing short of an environmental disaster.

"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."

He added that although the spill probably originated from a bus garage in Thornton Heath, the diesel was likely to have entered the river through a sewage treatment works.

A Thames Water spokesperson said: "Our teams attended as quickly as possible and placed booms into the river to minimise impact to wildlife and the environment and are carrying out an intense clean-up of our surface water sewers.

"Our teams will be working with the third party responsible for the pollution and we will continue to work alongside the Environment Agency and local authority to help resolve the issue as quickly and safely as possible."

The clean-up has been under way since Tuesday

A spokesperson for Transport for London (TfL) said a "full investigation" was under way into the leak.

"Protecting the environment is fundamental to everything we do and we are working closely with the Environment Agency, the London Fire Brigade and Merton Council to limit any environmental impact.

"Any pollution into London's waterways is completely unacceptable and we will play our part in tackling river pollution both from roads we control and our vehicle fleet," the spokesperson said.

The Wandle, which flows for nine miles from its source to the Thames, was for many years considered "ecologically dead", according to the South East Rivers Trust.

Now though, it is home to brown trout, a key chalk stream species, which was reintroduced to the river. The Wandle and its surrounding habitat also support wildlife including kingfishers, damselflies and bats.

Jack Hogan from the South East Rivers Trust said: "The real danger comes over the coming days, weeks and months, if not years, where this diesel breaks down into smaller particles and sinks down into the water.

"It'll start binding on to fish's gills, attaching itself to sediments, soaking into vegetation and banks, and diesel is highly toxic in those situations."

He added: "Until we really understand the scale of the impact of this, the best thing people can do is stay as far away as possible."

The public is being advised to stay clear of the contaminated water

Isobel Harris, from Friends of Poulter Park and Revesby Wood, said: "I hope that whoever is responsible for this is held to account.

"We cannot have organisations who are in a position to have this sort of accident that runs into our waterways."

Chalk streams, most of which are in England, are a globally rare habitat 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 flows through.

A spokesperson said: "We are closely monitoring the wetlands within the park and at Watermeads Nature Reserve, which is also cared for by the National Trust, for any visible impacts on the wildlife and rare habitats.

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

Additional reporting by Gem O'Reilly and Bhavani Vadde