There were thousands of fish deaths in a stretch of the River Thames between Kew and the Albert bridge on Sunday (June 5), when over 450,000 tonnes of storm sewage overflowed during heavy rain.
This deluge of polluted water in combination with the recent dry weather and subsequent low water levels led to a fatal drop in oxygen levels.
The Environment Agency (E.A.) is cleaning up along a 12km/7.5 mile stretch of the river, and adding oxygen in areas where dead fish and debris have been reported.
Species affected include flounder, bream, roach, eel and dace as well as other aquatic life.
An E.A. official confirmed that discharges from the combined sewer storm drain system happen typically between 50 and 60 times a year and can be caused by as little as 2mm of rain, but this Sunday's storm saw rain fall in excess of 30mm.
Storm sewage is the result of household and business sewage waste being mixed with rainfall run-off in the largely Victorian London sewage system. Thames Water is currently looking at various schemes for a new 32km (20mile) long 'super sewer' running from west to east London. However, even if approved the system is unlikely to be operational before 2020.
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