The European Union’s environment watchdog is to take legal action over wastewater overflows that resulted in the discharge of hundreds of thousands of tonnes of raw sewage into the River Thames over the summer.

The European Commission said that overflows into the river, which occur when the capital’s Victorian sewage system is unable to cope with heavy rain, were “too frequent and in excessive quantities”.

It is also taking action over storm water overflows on the seafront at Whitburn, Sunderland.

Stavros Dimas, the EU’s Environment Commissioner, announced the legal action yesterday, highlighting the Government’s failure to comply with EU waste water treatment legislation.

He said that untreated water not only posed a threat to human health but also to the marine environment. “More attention needs to be paid to upgrading collecting system,” he said.

The overflows, which are discharged into the tidal section of the Thames in West London, have been a longstanding problem for river users.

Rowers, canoeists and anglers say that they are forced to avoid some sections of the river during heavy rain because of the sludge. Concerns have been heightened because the river is to be used by rowers during the 2012 Olympics.

As the capital’s system is designed to absorb both sewage and rainwater, the contamination of the river occurs when treatment works and the sewer network are unable to cope with excess surface water during heavy rain.

In mid July, after heavy downpours, the Environment Agency said that 900,000 tonnes of sewage was discharged into the river. Only days before, more than 20,000 tonnes of raw sewage had gushed in the river at Kew, killing hundreds of fish

Although the discharge is approved by the Environment Agency, it is contrary to the European Urban Waste Water Treatment Directive, which requires wastewater to be collected and treated before discharge.

Thames Water says that the dumping into the river is the “least worst” solution as, otherwise, the material would back into London’s streets and homes. The overflows are allowed only in the river’s tidal stretch, in West London, as the fast flowing water absorbs bacteria.

Thames Water is expanding its sewage works near Twickenham by 40 per cent, which will reduce overflows by the beginning of 2013. It is also planning a “super sewer” to run under the river and improve capacity, although that will not be built until 2020.

A spokesperson for the Department for Environment, Food and Rural Affairs refused to comment on the specific case but said that it was “confident that water quality in the UK is at a consistently high level”.

The Commission will take action against Britain as a member state of the EU.

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