THE CURRENT SITUATION
At the moment, our sewers fill up when it rains - and untreated waste water spills out into the River Thames.
THE PROPOSED SOLUTION
The new "super sewer" would divert the waste water away from the river.
More top news
The creature was spotted in Hampstead Heath, the London Underground and the South Bank.
The problems appear to have been caused by a power supply problem in Queen's Park in north west London, which has affected signalling.
Cloudy conditions continuing overnight, with some patchy outbreaks of rain.