Last night's torrential rains led to 600,000 tonnes of raw sewage flooding into the River Thames, says a report from The Telegraph.
The discharge which The Telegraph says is equivalent in weight to "13 Titanics" (that's 6.0 1014 Schindleria brevipinguis in fishkeeping terminology) had to be released directly into the Thames to prevent London from flooding in the unusually heavy rains.
In order to prevent further fish deaths, the Environment Agency is adding hydrogen peroxide, an oxidising agent which boosts redox potential and rapidly raises oxygen levels. However, the sewage is expected to move along the Thames in the current for several days before the problem subsides.
An EA spokesman told The Telegraph:"The sudden downpour meant that London's drainage network could not cope and was overloaded.
"The storm sewage has resulted in vital oxygen reserves being used up, causing the fishkill - currently visible between Kew, Brentford, and Isleworth."