Swimmers are being warned to avoid the water at Ham, the first official bathing site on the River Thames in south-west London, due to the presence of toxic blue-green algae.
Blue-green algal blooms are uncommon in moving water but are believed to be caused by extreme heat, low river flow, and nutrient pollution from sewage. Thames Water's Hogsmill sewage treatment plant, situated three miles upstream of Ham, has previously been in breach of its permit conditions.
Marlene Lawrence of the Teddington Bluetits swimming group, which secured the bathing water designation for Ham, stated that this is the first time in nearly six years of swimming there that such algae has appeared. She noted that the river's flow is currently very low due to a lack of rain and high temperatures.
The Environment Agency, responsible for testing bathing water areas in England, has erected a sign at the site advising: “Do not enter the water. Do not let pets enter the water.”
The discovery of the algae raises further concerns regarding Thames Water's plans to pump 75m litres of treated sewage daily into the river near the bathing spot. This water recycling scheme is currently in the pre-application stage for a development consent order.