A £2bn tunnel will be built to prevent untreated sewage killing fish and polluting the River Thames, Environment Minister Ian Pearson said today.
The 18-mile pipeline will intercept sewage and rainwater run-off and carry it to be treated in East London.
The scheme, which will add around £37 a year to Thames Water customers' bills, is expected to be completed by 2020.
The tunnel is intended to catch the 52 million cubic metres of waste water which currently pollutes the rivers Thames and Lee each year.
London's 19th Century sewer network, which collects sewage and rainwater, is coming under increasing pressure from population growth and climate change.
Mr Pearson said: "Most Londoners would be shocked to hear that,because of an historic but increasingly outdated sewer network, a huge amount ofuntreated sewage and rainwater is spilling into the Thames at least once a week.
"This tunnel is the right solution for London and for the environment. Itwill give us a 21st century River Thames that we can all be proud of."