The River Thames has been flooded with more than a million tonnes of sewage in London in the past two days.
The drainage system pushes diluted sewage into the Thames
Heavy storms have been blamed for the sewage, which has caused a drop in the river's oxygen levels - threatening thousands of fish.
A "bubbler" vessel has been pumping tonnes of oxygen into the river between Vauxhall and Barnes, south-west London.
The Victorian drains force rainwater into the Thames through 60 overflows, to stop houses being flooded.
Proposals for a £1.5bn tunnel to intercept rainwater and take it to treatment works in east London, are still under consideration.
A Thames Water spokesman said the government had asked for further studies to be carried out, which are currently under way.
"We accept a long-term solution needs to be put into place, but we do not have the authority to give it the green light," he said.
Thousands of fish were killed in August 2004
Another "Thames bubbler" is being sent to Putney, south-west London.
And hydrogen peroxide has been released into the river near the Mogden sewage works, where oxygen levels have dropped to 20%.
Figures from the Environment Agency showed that on Tuesday night and the early hours of Wednesday, 853,000 tonnes of sewage was washed into the river.
The following night another 467,000 tonnes was pushed in.
Thousands of fish were killed in August 2004 when more than 600,000 tonnes of raw sewage was forced into the river. Many large fish were found floating in the water.
The Environment Agency said it had not yet noticed a similar effect from this week's storm, but it was possible smaller fish had been affected.