Going on a staycation this half-term? Swim at your peril after 46 Britishbeaches have been labelled potential health hazards in Britains' best-known seaside locations - with Blackpool topping the list as the worst offender.
Sewage discharged into the sea is generating dangerous levels of bacteria and viruses, according to the Marine Conservation Society, and no-swimming signs may have to be erected under European rules unless they're cleaned up.
There is, however, also good news: water quality around the coast is getting better in general.
The number of beaches recommended for excellent bathing water – 461 – is at the third highest level in the 24 years of the MCS Good Beach Guide.
But improvements are failing to keep up with the fact that the benchmark of acceptable bathing water quality is being raised.
The MCS explained that EU rules from 2015 will require the health warning signs on dirty beaches.
A spokesman told the Daily Mail: 'Forty-six UK beaches have failed to meet even the basic standards set 35 years ago in European law. These ... are a potential health hazard to beachgoers and could see swimming banned on them after 2015.'
Monitoring for the new EU standards begins next year.
If a beach consistently fails to meet its standards between then and 2015, signs will advise bathers not to enter the water.
Robert Keirle, MCS pollution programme manager, said there is particular concern about the amount of diluted sewage flowing into coastal waters from combined sewer overflows.
These act as emergency outlets for overloaded sewage systems during heavy rainfall. However, they can discharge at other times as well. Mr Keirle said there are 22,000 CSOs in the UK, but just a quarter are monitored.
'MCS wants all pipes mapped and monitored, and for the public to be told ... when, and for how long, the sewage is flowing,' he said.
'Mapping costs relatively little yet it could make the difference between an enjoyable trip to the beach or one that ends up in hospital with ear, nose and throat infections or stomach upsets.'
Responding to its bad results, Blackpool Council is adamant its water is safe, and said test results were affected by last year's 'promenade regeneration' programme.
'The water quality has improved significantly over the last ten years. Unfortunately the bar that we are measured against has also risen,' a spokesman said.
But Blackpool wasn't the only beach who needs to clean up. The top ten worst offenders were listed as: Blackpool, Morecambe, Heysham Sands, Looe, Instow, Lyme Regis (Church Beach), Aberdyfi, Barry (Watch House Bay), St Andrews (East Sands), and Ayr (South).
If you're prepared to head further afield, check out the most glorious beaches around the world below:
Swim ban on one in 10 British beaches?
Ten of the best beaches in Cornwall