London's ageing sewer network is already fighting the scourge of fatbergs, now one section faces a new battle, this time with a record-breaking "concreteberg" which is heavy as a blue whale.
The blockage, caused by people pouring concrete into drains, is the largest that water company Thames Water has ever seen and was discovered in Islington, north London.
Over time, the "concreteberg" has built up to become at least 100 metres long and weighs 105 tonnes.
The solidified concrete is more dense than a so-called fatberg, made up of fat, oil and wet wipes, and has set to the walls of the Victorian-era sewer.
Residents have been told the "concreteberg" will take at least two months to remove with pneumatic drills and high pressure jets, with work beginning next week.
Tankers will be kept on standby to pump out any backed-up sewage blocked by the concrete, Thames Water said.
Blockages cost Thames Water, the company that supplies water to London and the Thames Valley, around £18 million each year.
The concrete under Hall Street in Islington alone is expected to cost several hundred thousand pounds to clear.
Alex Saunders, Thames Water Operations Manager, said: “Normally blockages are caused by fat, oil and wet wipes building up in the sewer, but unfortunately in this case it’s rock-hard concrete.
“It’s in there and set to the Victorian brickwork, so we need to chip away at it to get it removed.
“This is not the first time damage has been caused by people pouring concrete into our sewers but it’s certainly the worst we’ve seen."
Reports of fatbergs have become a common occurrence in recent years as consumers and businesses flush wipes, fat and other food waste down drains instead of using bins.
Thames Water claims it is spending £1 million per month clearing blockages from its sewers in London and the Thames Valley – this amounts to an average of three fat-related blockages every hour.
In 2017, Thames Water discovered a fatberg weighing the same as 11 double decker buses and stretching the length of two football pitches was blocking a section of London’s ageing sewage network.
The congealed mass of fat, wet wipes and nappies in Whitechappel, east London was one of the biggest ever found.