Hounslow has been shamed as a fatberg "hot spot", and these grim photos illustrate the extent of the problem.
A fatberg is the name given to congealed masses of fat and wet wipe blocking pipes and causing sewage to back up into people's homes and gardens.
They have been responsible for an incredible 12,862 sewer blockages across the borough over the last five years, according to Thames Water.
That's more than 200 a month and, to put it into context, 1,300 more than during the same period in neighbouring Ealing, which is home to 80,000 more people.
Thames Water, which treats sewage from more than 15 million people across London and the Thames Valley, has named Hounslow as one of its fatberg "hot spots".
Even 'flushable' wet wipes can cause blockages
The utility firm has launched a campaign to prevent customers in the borough pouring leftover fat and used wet wipes down their drains.
Thames Water's head of customer field services, said: "Often people don’t realise the consequences of putting things other than human waste and toilet paper down their toilets and drains but it's time for everyone to understand and take action.
"It's not just fat that's the problem but wipes are a massive issue too. Many will be labelled as 'flushable' and they may disappear when you flush the toilet, but they don’t break down once they get into the sewer pipes."
Thames Water says it spends £1m a month clearing fatbergs, which cause sewage to back up into people's homes and gardens.
It hopes its Bin It - Don't Block It campaign will encourage people to put their cooking fat and wet wipes in the bin.
For more information about the new campaign, and how to dispose of cooking fat and wet wipes responsibly, visit the Thames Water website.