We call that the Fatberg in London, It's been an issue for the last few years due to fat/ grease from restaurants and homes being disposed of wrongly and I think it is illegal. On top of that, in the least few years, wet wipes and other bathroom products that don't dissolve are being disposed of causing issues.
We have a sewer system built in 1866 and even though it was future-proofed for the future, it has been way overcapacity. Currently, it is being upgraded with large engineering projects.
mus's comments