The Environment Agency believes most of the oil has cleared, but concerns over the impact remain unclear.
Members of the public were alerted by a video showing oil or fuel floating on water at Watermeads Nature Reserve, in Mitcham, was published on social media on Thursday (April 3).
The spill has been traced back to Poulter Park, but a cause has not yet been identified.
Residents passing the stream noted the oil sheen on the surface, as well as a notable smell emanating from the water.
Commenting on the post, Facebook user Claire Williams said: “The smell up at Mill Green and the factory estate is pungent of diesel.”
After receiving concerns and reports from the public, the Environment Agency (EA) acknowledged the incident.
On X, they stated: “We are continuously monitoring the River Wandle after the recent pollution. While we still get some reports of oil, we believe most of it has cleared.”
Bobby Dean, MP for Carshalton and Wallington, shared his concerns on X. He added that he is working with the Environment Agency, Thames Water, and the South East Rivers Trust “to determine the scale and cause” of the issue.
Mr Dean later told the Local Democracy Reporting Service (LDRS): “While it appears to be smaller than the environmental disaster we saw in February, the truth is we simply don’t know the full extent of the spill.
“What is clear is that this reinforces the vulnerability of the Wandle and the urgent need for independent pollution monitoring alongside better infrastructure.”
This incident marks the second incident of a spill on the Wandle.
In February, South London residents and conservationists were devastated to discover that an estimated 4,000 litres of oil had contaminated the historic chalk stream.
Mr Dean described this spill from a bus garage in Thornton Heath as an ‘environmental disaster.’ While the EA is continuing its investigation into that spill, many are concerned about its lasting impact on local biodiversity.
To make matters worse, the Watermeads area has been hit twice by spills this year, with the EA concentrating a clean-up operation on the Mitcham section.
In February, River Wandle expert Dr Jack Hogan told the LDRS of his concerns for the river.
He said: “It’s devastating, but we won’t know the extent of it yet. This damage is not just measured in days or weeks but potentially years. Judging by what we have seen, this is potentially the worst incident since 2007.”
The Wandle is one of the world’s purest chalk stream rivers and is home to many unique species. It starts life in Carshalton and Croydon before flowing into the River Thames at Wandsworth.
The EA continues the current spill and have encouraged anyone who sees pollution to report it to them on 0800 807060.
