HOW CLEAN IS THE RIVER THAMES ?
Statement from the Environment Agency to River Users Group 6 over sewage concerns at Little Marlow

Despite great improvements in water quality on the River Thames, there is still a potential hazard from sewer overflows that occur along the length of the river (not just in the tidal stretch). Sewer overflows are essential because they help prevent sewage backing up and flooding people’s homes when the sewers are inundated following heavy rainfall.

Some parts of the Thames are of a relatively high water quality. The quality varies at different places along the River Thames, and is dependent on the weather. Some of the sewerage treatment works overflows operate after only a small amount of rainfall; allowing untreated sewage mixed with rain water, to flow into the river.

Both treated and untreated sewage effluent can and does flow into the Thames. Treated sewage is not disinfected – it is just treated to remove solids and faecal matter.

The sewerage treatment works at Little Marlow receives raw sewage from the foul sewerage network, treats it to an acceptable standard and then discharges the effluent into the river.

The Environment Agency’s role is to ensure that these discharges are not harmful to the environment. Sewage discharges are regulated by an Environmental Permit, which defines the standard that the sewage must be treated to, with limits for ammonia, metals and biochemical oxygen demand (BOD).

BOD is the amount of oxygen in the water that the organisms need to break down organic material. Regular sampling is carried out to ensure the effluent meets the required quality. The permit also states where the discharge should be made from, how much sewage can be discharged and a range of other conditions. The permit conditions are set specifically for each sewage treatment works to make sure the risk is assessed thoroughly.

At Little Marlow, the pipe discharging final, treated, effluent has developed a fault. Environment Agency staff visited the sewage works on 4 February 2013 in response to a report of pollution from a member of the public.

We have been working with the Local Authorities Environmental Health team on subsequent checks; they are responsible for assessing risks to human health. Water quality results show very low ammonia, BOD and no solids or rag present. The sewage that has leaked onto the field is treated, and was destined for the River Thames. No extra sewage has entered the River Thames as a result of this fault.

The Environment Agency will continue to work with Environmental Health and Thames Water throughout the clean up process.

Swimming in the River Thames
There are risks associated with swimming in any open watercourse. Rivers are not sterile areas and there will always be some micro-organisms present.The Thames is not a designated bathing water, so it is not subject to the same water quality standards as designated bathing waters, which have to meet high quality standards to protect bathers health.

If people want to swim in the Thames, or other rivers, we would urge them to speak to the Health Protection Agency (HPA) for advice and guidance on swimming in rivers.

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