More than 243 billion litres of sewage has been pumped into the Thames in the last four years, the London Assembly Liberal Democrats have said.
Thousands of fish died after storms forced sewage into the Thames
They have called on government ministers to stop delaying a decision whether to back the construction of a tunnel which could ease the problem.
Thames Water says it would cost £1.5bn and will take 10 years to build.
The Liberal Democrats described the figures from January 2001 to November 2004, as an "absolute disgrace".
Dead fish were found floating in the river when heavy rain flooded the Victorian sewers in August.
'Cause for concern'
Mike Tuffrey, London Assembly Liberal Democrat spokesman for the environment, said dumping untreated sewage was "something that happened in the Victorian era".
"So much sewage being pumped into the Thames is bad for the environment, bad for human health and bad for the image of both the Thames and London," he said.
A Thames Water spokesman said the figures were a cause for concern but efforts were ongoing to try to alleviate the problem.
He said barges are used to pump oxygen into the river and a chemical which boosts oxygen levels, both help to counter the effects of pollution.
A spokesman for the Department of Environment, Food and Rural Affairs said ministers had asked for a further study into the proposed tunnel.
He said in the meantime money was being invested into treatment works and smaller scale measures to tackle the problem.
The tunnel - running along the course of the river - would intercept rain water and take it to treatment works in east London.