River health
Rivers are essential to the health of our natural environment, yet many of London's rivers are polluted. Only one of London’s 41 river water bodies is classed as ‘good’ – three are ‘bad’, five are ‘poor’ and the rest are ‘moderate’ under the EU Water Framework Directive.
This means that our rivers are much less healthy than they should be, and it means that key species like eels and barbels (a freshwater fish) struggle to survive in London’s rivers.
- The Environment Agency oversees water quality issues, including monitoring and regulation.
- Water companies have a responsibility to prevent pollution incidents and mitigate the impacts when pollution occurs.
- London boroughs have responsibility for the enforcement of the proper maintenance of the road drainage network.
- Catchment Management Partnerships have been established to actively involve communities in improving local water quality.
Context
Inner London. Many parts of inner London have sewer systems that carry rainwater as well as sewage. These Victorian 'combined sewer systems' were designed for a city of four million people. But with sewage from almost nine million people, the network is now at 80 per cent or more of capacity, even in dry weather.
Outer London. Even in parts of outer London where there are separate pipes for carrying rainwater, there are significant capacity and water quality problems.
The main problem is too much rainwater reaching the sewer system. That's why the Thames Tideway Tunnel is being built. It will help reduce the amount of untreated sewage that is released into the Thames. To view other projects that have been delivered or opportunities that could help improve our rivers, visit the London Rivers Map.
Visit the London River Health map to see what type of sewer system is in your area and the issues facing London's rivers.
If you see river pollution please report it to the Environment Agency and Thames Water.
Sewer overflows
Sewer (or storm) overflows are a designed feature to prevent sewerage from backing up into homes in the event of exceptionally heavy rainfall. There are more than 100 sewer overflow sites across the capital.
The Urban Waste Water Treatment Directive states that sewer overflows should only be used in “exceptional circumstances” such as extreme weather conditions or exceptional rainfall. However, we are increasingly seeing discharge notifications issued during what many would consider to be normal rainfall events.
Visit the London River Health map to see the sewer overflow locations in London.
Misconnections
Misconnections are where a property’s wastewater is wrongly connected into rainwater downpipes meaning toilet waste and waste water from dishwashers, washing machines and sinks can discharge into local waterways.
Misconnected properties are a major cause of poor water quality in rivers and can be very harmful to local wildlife.
Plumbing misconnections are usually easy to fix and are the responsibility of the property owner. ConnectRight has further advice on spotting a misconnection and finding a WaterSafe plumber to fix it.
Misconnections tend to be more common in areas where there is a separated sewer system, usually outside of central London which is covered by the capital’s historic combined sewer system (collecting waste water and rain water).
The Zoological Society of London and charity Thames 21 run Outfall Safaris, citizen science pollution monitoring events. The data from these events and data from the Environment Agency has been used in the London River Health map to show where pollution has been reported.
Road runoff
A key source of river pollution is ‘road run off’. This pollution occurs when pollutants that settle on the road build up during dry weather events and are then washed into nearby rivers and streams when it rains. The pollutants get deposited onto the road from residue from oil spills and from tyre and break wear from vehicles.
It has long been one of the most challenging pollution issues to identify, quantify and resolve. A problem that is likely to get worse with a changing climate.
Road Pollution Solutions
The Mayor has partnered with the Environment Agency and the Zoological Society of London to fund Thames21 to develop a new model, which uses numbers and types of vehicles to predict the amount of pollution deposited on roads and the degree of damage to our rivers. The project was also in partnership with Middlesex University, Transport for London, Thames Water and South East Rivers Trust.
Phase 1
The first phase of the study, which took place in 2019, identified roads of varying level of priority that had the greatest potential to contribute towards pollution in London’s rivers. This then helped to identify the best locations for interventions to address this issue. To find out more about phase 1 please see the Road Runoff Water Quality Study Executive Summary.
Phase 2
In 2023, the second phase of the project produced a decision support tool. This tool was created to show varying levels of pollution, and identifies the best locations for nature-based solution interventions to address this issue of road runoff pollution.
The British Geological Survey, as part of the Community Water Management for a Liveable London (CAMELLIA) programme have played a vital part in bringing the underpinning model to life and developing the visualisation for a user friendly decision support tool.
The modelling is limited to the larger roads and rivers as a result of the data available. It is also limited to outer London due to the separate surface water drains present here. The modelling project provides the prediction pollution concentrations for 3,884 km of roads around greater London.
You can access more information about the project with the decision support tool on the Thames21 website.
The results of this project will help to inform further work by the GLA and partners to identify the most appropriate type of roadside sustainable drainage systems and identify new opportunities for wetland creation for priority locations. These interventions can also provide a host of additional benefits in these locations, including: reducing flood risk, improved amenity, greater biodiversity and localised air quality and cooling benefits. These solutions can be integrated into future highways works.