Domestic waste water pipes misconnected to surface water drains are leading to sewage and chemical pollution on every kilometre of London's rivers, a major study has found.
The findings have led ecologists who carried out the survey to call for local authorities to ensure the plumbing systems of new developments meet correct standards.
The study, conducted by the Zoological Society of London in partnership with the Environment Agency, Thames Water, Thames21 and Catchment Partnerships in London, rivers found an average of 2-3 polluting outfalls for every kilometre of Greater London's 600km river system.
Contamination including sewage fungus was found at 356 of 1,177 outfalls assessed, along with definite pollution problems in 269 cases.
The data indicates a large number of properties across London are sending foul waste from toilets, sinks and washing machines into rivers via the surface water drainage system, rather than to sewage treatment works.
Joe Pecorelli, project manager for ZSL's estuaries and freshwater tea called for a significant increase in investment to address misconnections in household and commercial plumbing systems across London.
He added: "We're also asking local authorities to ensure the plumbing system of new developments meet correct standards, and that funding is increased for industry-wide awareness schemes like ConnectRight."
Poor water quality, badly-designed flood defences and adaptations for navigation mean only one of the 39 rivers in Greater London has so far qualified as having 'good' ecological status or potential under the Water Framework Directive legislation.
The data for this report was collected by teams of volunteers using specially-created app to geotag, photograph and assess outfalls for evidence of pollution. The data was analysed by ZSL, and reported to the Environment Agency and Thames Water.
Debbie Leach, chief executive of waterways charity Thames21, said: "Each day, more and more waste water pipes from our houses are being connected up to rainwater drains going straight into rivers, and the result is horrendous."
For more information and to read the final report by ZSL, click here.