A new project aimed at improving flood resilience and water quality at Leg o' Mutton Nature Reserve has been approved by Richmond upon Thames Council.
The scheme, part of the wider Community BlueScapes programme funded by DEFRA, will divert surface water runoff from the surrounding catchment into the reservoir. This will help to top up water levels, particularly during dry summer months, and increase storage capacity to reduce flood risk during high tide events. The proposal is designed to maintain the reservoir at a maximum operating water level of approximately 2.5 metres
, ensuring sufficient freeboard and flood storage capacity are always maintained
. Climate change is expected to exacerbate existing water level and quality issues due to hotter, drier summers.
Currently, the Leg o' Mutton reservoir suffers from low water levels in summer, leading to high temperatures and deoxygenation, which negatively impacts its ecosystem. The existing method of topping up with water from the River Thames introduces invasive species and sediment. Specifically, inappropriate species such as invasive Zebra Mussels and protected European eels are introduced, with no means of escape from the lake. Furthermore, sediment from the Thames has built up to approximately 50cm on the lake bed, creating an unsuitable substrate for many aquatic plants.
The new nature-based solution will incorporate sediment capture and reedbed filtration to improve water quality before the water enters the lake. The reedbed filtration system aims to provide natural filtration and improve water quality through particle entrapment and microbial action, seeking to achieve Water Framework Directive (WFD) standards over time. It is also designed to reduce hydrocarbons and other pollutants from road drainage systems. A fixed spillway will also be constructed to allow controlled overflow back into the River Thames. The spillway is designed to maintain the reservoir at its maximum operating level of 2.5 metres, with the exact level to be confirmed with the Environment Agency.
Lizzie Bunker, Lead Local Flood Authority Manager for Richmond, explained the project's dual benefits: The proposal therefore delivers multiple benefits by combining flood risk management with biodiversity enhancement and sustainable water management.
The project is expected to reduce flood risk to nearby roads and properties, improve the long-term water level management within the reservoir, and enhance the ecological condition of the nature reserve. Specific biodiversity enhancements include improving aquatic and fish life, which will in turn benefit waterfowl, predatory birds such as herons and cormorants, and overwintering species.
Project development costs to date total £156,191.63, with project delivery costs anticipated to be up to £395,000. These costs are covered by the Community BlueScapes programme funding from Defra's Flood and Coastal Innovative Resilience programme, which concludes in March 2027. If the project cannot be delivered before this date, an alternative funding source will need to be secured.
Construction is anticipated to take approximately two months, with delivery planned for late 2026 to early 2027, outside of the bird nesting season. Measures will be in place to mitigate disruption to local wildlife, with vegetation clearance managed to avoid impacts on nesting birds. During construction, Ferry Lane will be closed, and pathways around the lake will have restricted access.