A 100-metre “concreteberg” weighing the same as a blue whale came to block three major sewers beneath the streets of Islington – spelling travel mayhem for Islington neighbours until at least June.

Islington Gazette: Concreteberg beneath streets of Islington. Picture: Thames WaterConcreteberg beneath streets of Islington. Picture: Thames Water (Image: Archant)

Thames Water says it will take an “industrial” scale operation involving pneumatic drills and high-pressure jets to destroy the concrete blockage, estimated to weigh 105 tonnes, and this will cause major traffic disruption to Goswell Road and Hall Street.

This huge undertaking to remove the concreteberg, which water bosses say is the biggest they’ve ever encountered, will commence next week and it will cost at least several hundred thousand pounds, but potentially up to £1million to remove. Tanker pumps are on standby and can be deployed 24/7 to protect the environment, and ensure neighbouring properties and businesses are not flooded with sewage caused by the rock-hard mass.

Alex Saunders, Thames Water operations manager, said: “Normally blockages [like fatbergs] 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. It’s very frustrating and takes a great amount of time and effort to resolve. We’re now doing everything we can to deal with it as quickly as possible, making sure our customers don’t have to suffer because of this mindless abuse of our network.”

It’s understood Thames Water will take legal action to recoup costs it identifies the person or persons responsible for concrete being in the sewer.

In May last year a Hoxton construction company flooded sewage pipes with concrete, but Thames Water told the Gazette this incident is not being investigated as linked.

The Green Party London-wide Assembly Member Cllr Caroline Russell said: “This is a scandalous blockage. It’s hundreds of cubic metres of concrete. That’s not someone casually cleaning out a bucket, its far more likely to be a concrete pour to a development that has gone disastrously wrong. What’s shocking is that no one even noticed they’d lost so much concrete.

“Cleaning this up will take a couple of months and while that is happening local residents are at risk of their homes being flooded with sewage whenever there is heavy rainfall and high surface water run off. And all local roads will experience massive lorries removing the concrete as it gets broken up.

“I’m sure Thames Water will work hard to protect local homes from sewage and I hope they can track down the culprits so Londoners don’t have to pay to clean up this concrete vandalism through our water bills.”

Every year Thames Water, serving 15 million people across London and the Thames Valley, spends £18million clearing blockages from its sewers. The company has pledged to invest heavily to improve the network and increase monitoring as part of its business plan for 2020-25 – using up to 200,000 new sewer depth digital monitors. It has also proposed to reduce pollutions by 30 per cent.