The removal of a “monster” fatberg that “looks like something out of a horror scene” is set to begin in a Devon seaside town.
South West Water staff were seen wearing breathing apparatus as they descended into the sewer in Sidmouth on Tuesday.
The workers have been carrying out a 3D scan of the 64m (210ft) mass of hardened oil and wet wipes, which is longer than four double-decker buses.
It was discovered in December and could take up to eight weeks to remove.
Sewer workers will use high pressure water hoses and pick axes to break up the mass, with jetting equipment deployed to suck the fat up to tankers on the surface.
The waste will be processed and turned into green energy.
South West Water said in a statement on its website: “Fortunately, the fatberg has had no impact on Sidmouth’s excellent bathing water quality and has been discovered in good time.
“But it doesn’t always end this way.
“Every time a wet wipe is flushed or oil poured down the drain, there is a risk these items could cause sewer blockages.
“This is extremely unpleasant and could happen in your own home.
“We tackle dozens of new sewer blockages every day, which adds £4.5m to bills every year.”
High levels of hydrogen, sulphate and methane mean the air is too unstable to risk bringing cameras down to film the removal, South West Water has said.
Fatbergs form when people flush waste such as fat, nappies, wet wipes and sanitary towels down their toilets.
South West Water advises: “Stop the block by only flushing the three Ps – pee, paper and poo – and by not pouring fat, oil and grease down the drain.”
The work marks the first time the water firm has tackled a fatberg on this scale.
A spokesman said the clearance would have to be carried out in “exceptionally challenging conditions”.
Chris Ewart, 51, from Plymouth found the fatberg while carrying out an inspection of the sewers under Sidmouth.
He told Plymouth Live: “I saw it and thought ‘what on Earth?’ it was completely unexpected.
“It’s really eerie in that bit of the sewer and it does look like something out of a horror scene, all congealed and glossy and matted together with all kinds of things.”