A 64-metre-long blockage of fat, wet wipes and grease has been found in a Sidmouth sewer under The Esplanade.
The so-called 'fatberg' as it's being dubbed would be taller than the Leaning Tower of Pisa.
South West Water say it's the biggest they've ever found.
Work to remove it will start next month and could take eight weeks.
Director of Wastewater Andrew Roantree said: "It shows how this key environmental issue is not just facing the UK's cities, but right here in our coastal towns.
"It is the largest discovered in our service history and will take our sewer team around eight weeks to dissect this monster in exceptionally challenging work conditions.
"Thankfully it has been identified in good time with no risk to bathing waters.
"If you keep just one new year’s resolution this year, let it be to not pour fats, oil or grease down the drain, or flush wet-wipes down the loo.
"The consequences can be significant - including sewer flooding in your own home.
"Put your pipes on a diet and don’t feed the fatberg.
"A fatberg forms like a snowball - as wet-wipes get flushed down loos, fats oil and grease congeal together, gradually forming a hard mass known as a fatberg.
"The removal is due to start on Monday 4 February, but heavy rain could cause delays.
"Sewer workers will require full breathing apparatus to carry out the removal, which will involve a combination of manual labour and special sewer jetting equipment.
"Nearby businesses will not be affected by the removal and the esplanade will remain fully accessible with no impact to traffic."