Oxford city centre 'fatbergs' caused by food outlet oil
Oxford has persistent problems with "fatbergs" because only 5% of food outlets are correctly disposing of oil, fat and grease, Thames Water has said.
The company said more than 20 tonnes of fat and waste end up in the city's Park End Street sewer alone each year.
Thames Water said it mixes with waste such as wet wipes and hardens, blocking the city's sewer system.
The company found 80% of 200 eateries surveyed did not have any grease-trapping equipment.
Spokeswoman Becky Trotman said in Oxford the problem "seems to be getting worse" and a blockage the size of two double-decker buses was removed in February.
She said food outlets are being urged to fit grease-trapping equipment that prevents oil from being washed into the city sewers.
A further 15% of food outlets were found to be using ineffective grease traps, while less than half of managers and owners surveyed knew what they were.
Thames Water regional manager Sean Walden said: "It was particularly useful to speak to business owners about their responsibilities.
"The majority are keen to learn more about what they can do to help reduce fatbergs, which is really encouraging."
In 2014 a fatberg caused the sewer under Hollybush Row to collapse and work to remove it caused caused traffic delays in the centre of Oxford.