Storms Devastate Thames Fish Stock

450,000 tonnes of sewage lead to wildlife catastrophe

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Environment Agency officers are supervising the clean up of the River Thames in West London following the discharge of over 450,000 tonnes of storm sewage over the weekend.

Large numbers of dead fish including flounder, bream, roach, eel, dace and other aquatic life such as water shrimps have been spotted along the river along with sewage detritus.

The incident happened after the heavy rain over the weekend caused the release of more than 250,000 tonnes of storm sewage into the river from combined sewer overflows (CSOs) and at least 200,000 tonnes of storm sewage from the Mogden Sewage Treatment Works in Isleworth. These discharges, combined with the current warm dry weather and low river flows, resulted in the low oxygen levels and fish deaths along a kilometre stretch of the river

Oxygen levels are being studied by Environment Agency monitoring stations along the river. Thames Water has dosed the polluted water with hydrogen peroxide from three different locations to add oxygen to the water. Its oxygenation vessels have also been deployed to the area and can inject 30 tonnes of oxygen a day into the water.

Howard Davidson, the Environment Agency’s Director, South East said: “This is a major sewage pollution incident which has caused the death of a huge number of fish. Discharges from combined sewers happen 50 to 60 times a year and can be caused by as little as 2 mm of rainfall, and on Sunday more than 30mm fell over west London.

“We are currently monitoring Thames Water’s clean up efforts and assessing the full impact but unfortunately we may never know the exact numbers of fish that have died.”

The Environment Agency has worked with Thames Water and other partners to find a solution to these discharges. The London Tideway Improvements Programme which will reduce such storm sewage discharges to the Thames, involves upgrades to all the major tidal sewage treatment works to increase their capacity, and the proposed London Tideway Tunnels which recently underwent a public consultation.

Members of the public can report pollution incidents by calling the Environment Agency’s emergency hotline on 0800 80 70 60.

June 7, 2011