Thousands of litres of sewage are being pumped into the sea from blocks of flats with misconnected pipes every day, according to a water firm.
In the last few weeks, Southern Water said a block of 16 flats was found in Worthing, West Sussex, where eight homes' waste was going into the ocean.
The water firm's workers said this was not the only building where it was happening, and more had been discovered this week.
Campaign group Surfers Against Sewage claimed the firm was engaging in a PR stunt by publicising the matter, but Southern Water said the causes of poor water quality were "complex and varied" and "misconnections can have a very significant impact".
Southern Water said the waste was ending up in the sea because it was being sent into surface water drains instead of the sewage system.
An Environment Agency statement on its bathing water quality report for Worthing Beach House, the bathing site near the block of flats, also said the main source of contamination for the area was likely "urban diffuse pollution entering through the surface water system".
Southern Water's Phil Cresswell-Nash said: "There is a dedicated team purely for Worthing, to be able to look at these misconnections.
"So, with this one being found, we're confident the team will be able to find more and reduce the amount of surface water that's going out into the seas, to actually reduce and improve the bathing water quality across the coast."
His colleague, Will Curtis, is one of a group of so-called "Sewage Sherlocks" who work to track down sewage leaks.
He and his colleagues put dye down sinks and toilets to confirm whether a flat is connected properly to the sewage system.
If the dye goes into the surface water network, the flat is wrongly connected.
Curtis said: "We had eight properties which were flushing their toilet numerous times a day.
"It [flowed] straight through the surface water line... and went straight into the sea."
He said it would have had a "huge" impact on the quality of bathing water.
His colleague, Pete Booth, said finding misconnected properties could be like looking for a needle in a haystack.
"It can take days, weeks, it can take a very long time," he said.
"Sometimes we're lucky. We can find it straight away. But other times it takes a lot more investigation."
Southern Water has been at the centre of a number of incidents, including in January when millions of plastic pellets were washed up on the Sussex and Kent coast.
In 2019, it was hit with a £126m fine for wastewater spills, and then £90m in fines in 2021.
Last April, it pleaded guilty to 13 sewage spills in Kent.
Surfers Against Sewage, however, was unimpressed with Southern Water's work.
Chloe Flood from the campaign group said: "This is pretty outrageous from Southern Water.
"We see this time and time again. If it's not the weather, it's us that are the problem.
"This is nothing more than a PR stunt to shift the focus away from the real problems with Southern Water themselves."
A spokesperson for Southern Water said it "engages closely with members of Surfers Against Sewage", adding: "The causes of poor water quality are complex and varied - road run off, animal life, human behaviour on beaches. Misconnections can have a very significant impact."