The Good Beach Guide saw a decline in beaches rated "excellent"
The recession, a weak pound and an increasing awareness of carbon footprints have combined to help resurrect the British seaside holiday, now known as the "staycation".
But as the barbecue summer of 2009 was washed away in the heavy rains of a decidedly soggy July, those who campaign to ensure Britain's beaches are clean and safe have grown increasingly worried.
Of all the beaches tested for water quality in the UK, 43% present at least a one in 20 chance of getting gastroenteritis after a swim, according to a calculation by the Marine Conservation Society (MCS). The odds are derived from World Health Organization figures.
For bathing water that just passes the minimum legal standard, the odds of falling ill can be as high as one in seven.
Thomas Bell, coastal pollution officer for the MCS and editor of the Good Beach Guide, said the latest available figures reveal a decline in quality over the past three years, with the number of beaches in the guide recommended as 'excellent' down by almost 17% over 2008.
The drop represents the biggest year-on-year fall in the Good Beach Guide's 22-year history.
The culprit is the weather, as rainfall washes waste into the sea from a variety of sources, including agricultural run-off.
When sewage treatment plants are overwhelmed by heavy storms, water companies are allowed to employ what is supposed to be their weapon of last resort - combined sewer overflow pipes - or CSOs.
There are more than 20,000 CSOs around the UK, all owned and operated by UK water companies.
In theory, they are meant to act as safety valves for the system during periods of intense and heavy rainfall. They combine storm water with raw sewage and spill out of CSOs into rivers and eventually into the sea.
For most people on a day out at the seaside, steering clear of a nearby CSO would be a priority and the Environment Agency recommends that people avoid bathing for 24 hours after heavy rain.
But, according to the Good Beach Guide, 45% of the 1,134 beaches they list have a CSO close enough to affect them.
And the MCS's Mr Bell said some of those CSO are spilling more often than most people realise.
"We do know that on some beaches, these CSOs are discharging all the time, up to hundreds of times a year," he said. "It's more than possible that we've built ourselves a system in this country where they're being used as a means of regular sewage disposal."
Miranda Kavanagh, the director of evidence for the Environment Agency, the government body which polices the pipes, said: "The alternative is to have sewage backing up into people's homes and up the street...it's a matter, for us, of balancing risks to public health against risk to the environment and trying to find a balance between those two things. It's not a black-and-white situation."
If a problem is detected in bathing water quality, the Environment Agency says it carries out more testing and takes action to remedy the situation.
Andy Cummins of the advocacy group Surfers Against Sewage, said: "We've had people call us from Wales, from Scotland, from the northeast and from the southwest telling us about how they've contracted illnesses after rain, how they've noticed raw sewage and sewerage related debris in the sea.
"It's filthy, you are surfing in a sewer."
The recent decline in beach quality comes after massive improvements were made since the early 1990s - with an estimated £8bn spent by water companies over the past 20 years - as Britain worked to comply with the European water directives that dictate acceptable water-quality levels.
The EA's Ms Kavanagh said CSO sewage spills that are not deemed to be a risk to bathing water do not need to be reported. The EA grants consent for limited spills when necessary.
Spills directly onto designated beaches are limited to three times a year, but those upriver, which flow onto nearby beaches, are given more leeway
"If it is within consented limits and has no impact on the bathing water quality then unless we have particular concerns that would not necessarily be something that would come to our attention.
The MCS's Mr Bell said the bigger concern is that the general water quality testing system approved by the EA does not take the impact of CSOs into account.
Surfers have complained of falling ill and finding sewage debris
"There is no - at the moment - testing regime in place to monitor on a systematic basis for discharge from those pipes."
The travel writer Bill Bryson added his voice to the call for a more general coastal clean-up.
Bryson, the current president of the Campaign to Protect Rural England, said: "Britain is blessed with beautiful countryside, a breathtaking coastline and wonderful beaches.
"It is really alarming that over the past 10 years beach litter has increased by 80% and it is beyond comprehension how we can allow this continued trashing of a national asset. We really should be putting more effort into keeping our coast and countryside clean."
Panorama: Britain's Dirty Beaches, BBC One, Monday, 7 September at 2030 BST.