Chamber Mead Wetlands

We are building a series of wetlands to help conserve the Hogsmill River – a much-loved chalk stream. This includes cleaning 250 million litres of water through natural systems to combat pollution.

This project is part of a wider partnership between the Rivers Trust and The Coca-Cola Foundation to help clean some of Britain’s most polluted rivers, reduce flood risk, and to create new wetland habitats in both rural and urban locations across the country, replenishing 1.6 billion litres of water.

  • Delivery expected


Work timescales

Work to create this wetland started in August 2023 and is now expected to run until early December 2023.

Parking restrictions will be in place at two locations along the Green Lanes during the works, to allow site access for vehicles involved in the construction phase.

The work will also require a large number of lorry movements to remove excavated material from the site. We thank the public for their patience and understanding during the construction of the project.

Planning permission was granted in July 2022.

The application received lots of support.

“What an excellent plan to improve the water quality while at the same time making improvements for wildlife in the area.”

If you wish to speak to us about the project, please email us at

Chamber Mead wetlands during construction

Project update 7th November 2023

Lots of progress has been made since the August start. The poor weather has been challenging. Heavy rainfall / surface water entering the wetlands during construction has led to some programme delays and putting back the completion date to December, but work is continuing.

Once the project is completed:

  • Water will flow along the Green Lanes Stream, but instead of running straight into the Hogsmill River it will be diverted through a sediment trap and two wetlands. At the other end, the wetland will be connected into the Hogsmill River, downstream of the stepping stones
  • The wetlands will add variety of habitat and amenity benefit to the Hogsmill Local Nature Reserve, as well as improve water quality for a 200 metre section of rare chalk stream
  • A footbridge over the newly created channel will be added to ensure continued access around the Chamber Mead area for members of the public. The footbridge will be located close to the stepping stones
  • The wetlands will be planted with a range of diverse plant species, informed by a wetland specialist. The banks of the wetlands will be fenced off to protect the wetlands and to give plants time to establish. The wider open space will remain accessible to the public
  • Information boards about the project and new benches will be added to the area
  • Some vegetation removal has been necessary to allow the works to go ahead. A number of trees will also be planted as part of the project. These include disease-resistant Elms, which will benefit a local population of White-Letter Hairstreak butterflies.
The shaded area shows where the Green Lanes Stream will be blocked and diverted through the wetlands

Why the Hogsmill?

The Hogsmill River is a cherished chalk stream in south London. Flowing through the Hogsmill Local Nature Reserve in Ewell, the river is very popular with families and dog walkers.

Chalk streams such as the Hogsmill are globally rare habitats, of which there are estimated to be only 210 worldwide. These special rivers give rise to a unique set of species that depend on the clean, chalk-purified water and are very sensitive to pollution.

Sadly, the Hogsmill has poor water quality – suffering pollution from a range of sources.

© South East Rivers Trust

A poo-luted river

The Green Lanes Stream tributary joins the Hogsmill a few hundred metres downstream from its source. This tributary brings with it a cocktail of pollution, receiving road runoff from Epsom town centre and nearby industrial areas.

During heavy rainfall the river can also be impacted by discharges of untreated sewage and stormwater from the Epsom Storm Tanks.

This pollution is not only a threat to the chalk stream but also poses a public health risk to children who play in the river and to dogs and their owners.

Polluted water from the Green Lanes Stream entering the Hogsmill chalkstream © South East Rivers Trust

Wonderful wetlands

Wetlands are a nature-based solution to improving water quality. Water that drains through wetlands is gradually filtered by plants and captured in the soil, intercepting and treating pollution.

The Chamber Mead Wetland will do exactly that. It will intercept the Green Lanes Stream, filter and clean the water through a series of wetlands before rejoining the Hogsmill with cleaner, safer water.

Wetlands provide multiple benefits. They sequester carbon, provide flood storage, mitigate the impacts of droughts by storing water in the landscape, and boost biodiversity.

Image by Meatle from Pixabay

A partnership project

Chamber Mead Wetlands is a collaborative project led by the South East Rivers Trust. Our partners include the Hogsmill Catchment Partnership, the Environment Agency, and Epsom and Ewell Borough Council.

The partners have completed a feasibility study investigating how water quality from the Green Lanes Stream can be improved at the same time as improving open space within the Local Nature Reserve for people and wildlife.

The favoured option involves diverting the Green Lanes Stream through Chamber Mead meadow. The new channel would follow a winding path, passing through a constructed sediment trap and wetlands, before entering back into the Hogsmill river approximately 200 metres further downstream.

© South East Rivers Trust

What will change?

The project will bring multiple benefits to the Hogsmill’s health and ecology, provide varied habitat and increase biodiversity, benefit public health and boost local amenity value.

The project will result in:

  • Improved water quality
  • Reduced risk to health from contaminants and sewage based pathogens
  • An extra 200m of un-impacted chalk stream habitat
  • Up to 2,000m2 of wetland habitat created
  • Enhanced aesthetic value and reduced visible pollution
  • Outdoor educational opportunities for local schools
  • Improved community amenity with the new wetlands forming an attractive addition to the Hogsmill Local Nature Reserve.
Image by 16081684 from Pixabay

Thanks to our supporters

Coca-Cola Europacific Partners
The Coca-Cola Foundation
Epsom & Ewell Borough Council
The Rivers Trust
Thames Water
Environment Agency logo
Garfield Weston
Surrey County Council logo