27 April 2017 Last updated at 06:48 BST
The Victorian sewage tunnels which carries waste water and sewage from your homes and schools are struggling to cope.
When they were made, over 150 years ago, four million people lived in London. This has since doubled and so has the waste.
When the system can't cope the extra waste runs straight into the River Thames... urrghhh!
So a new super-sewer is being created to tackle the problem. A tunnel running under the city will transport the waste from your home to a treatment works.
It's going to take seven years to complete the project and will cost a lot of money, but when it's finished no more sewage will be running into the Thames!
London has a bit of a blockage and it's making a bit of a stink!