Water Quality

Rivers are essential to 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 (EA) 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 building regulations, correction of misconnections, proper maintenance of the road drainage network, and the reduction of run-off by promoting sustainable drainage through the planning process. In addition, a number of Catchment Management Partnerships have been established to actively involve communities in improving local water quality.

Road Runoff Water Quality Study

A key source of river pollution is ‘road run off’. This occurs when pollutants that settle on the surface of the road, such as residue from oil spills, as well as tyre and brake wear from vehicles, build up during dry weather and are then washed into nearby rivers and streams when it rains.  A problem that is likely to get worse with a changing climate.
The Mayor has partnered with the Environment Agency and Transport for London (TfL) to fund Thames21 and Middlesex University to develop a new model, which uses numbers of vehicles and types to predict the amount of pollution deposited on roads and the degree of damage to our rivers. The project was also supported by the Zoological Society of London, Thames Water and South East Rivers Trust.
The study has identified those roads that have the greatest potential to contribute towards pollution in London’s rivers to help identify the best locations for interventions to address this issue. The modelling is limited to outer London, because in outer London there is a separate surface water system. Surface water is rainwater that collects from roofs, driveways, drains and gutters. In outer London it drains directly to rivers through a separate surface water sewage system, whereas central London has a combined drainage system, where surface water drains alongside domestic foul water pipes to sewage treatment works.
The modelling for this project only applies to the major roads in outer London for which TfL have modelled or observed data around vehicle movements. This equates to nearly 40,000km, 75 per cent of London’s major roads.


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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.

To find out more about this project please see the Road Runoff Water Quality Study Executive Summary.

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