Since early summer, the water has shown exceptionally high levels of enterococcus bacteria - a polite way of saying it is infested with human faeces - keeping the surfers, the perfectly toned beach lovers and just about everyone else well away. At first, just one section of the beach was cordoned off but, as the summer has blended into early autumn, all eight miles of the fabled stretch of Pacific shoreline have been deemed off limits.
Earlier this month, officials declared Huntington Beach safe in time for the Labor Day weekend, but they have since closed it again after finding bacteria levels four times greater than the safety limit.
And Surf City is not the only oceanside paradise turned bad. Surfrider Beach in Malibu has become so riddled with E. coli bacteria and enteric viruses that it has been all but abandoned.
One might not expect the ocean immediately adjacent to a giant metropolis such as Los Angeles to be pure, but the risk of infection stretches far beyond the city limits - starting at the rugged coastal wilds at the north- western end of Los Angeles County and stretching all the way past San Diego to the Mexican border. And if the surfing beaches are bad, the rest are even worse. For example, Aliso Creek in Orange County, part of the endless southern suburbs of the city, has registered pollution levels 100 times worse than Huntington Beach this summer.
The reason, it seems, has nothing to do with faulty sewage treatment or factory effluent. Although the precise cause of the contamination of Surf City has yet to be identified, it is almost certainly the result of "urban run-off" - that is, the common detritus that is flushed into storm drains and siphoned directly into the ocean.
In a city built overwhelmingly on concrete, the storm drains fill with everything from motor oil to dog excrement, by way of garden pesticides and swimming pool and septic tank chemicals. The Ballona Creek, which collects the run-off from most of downtown Los Angeles and spills it straight out into Santa Monica Bay, is filled with the faeces of tens of thousands of homeless people living on Skid Row, which the city dutifully hose down each day.
As for heavier pollutants, more oil seeps into the water from leaky private cars each year than from the worst tanker spill, according to John Hoskinson of Surfrider International, a group combiing sporting and environmental concerns. "All these things are basically the result of over-concretisation," Mr Hoskinson said. "We've built and built with minimal planning restrictions and this is the result."
Contamination levels have swelled 12-fold in the past 27 years, according to figures cited recently by the Los Angeles Times. The LA area now pumps out about one trillion gallons of bacteria-infested water each year, roughly the capacity of two swimming pools for every citizen. According to a 1995 study, one in 25 people who swam near a storm drain came down with a gastrointestinal illness.
When it rains, the problems are instantly compounded: one inch of rain results in an estimated two tons of extra garbage in Ballona Creek. Environmentalists suggest no one should swim in the Pacific for 72 hours after a rainstorm.
Some local authorities are working to remedy the situation. The city of Santa Monica, for example, now diverts its storm drains into the sewage system and is building an $8m (pounds 4.9m) treatment plant next to the pier to deal with the extra load. This is, however, only a cosmetic and highly limited solution. City officials admit they can divert the drain water only in the dry summer months. To deal with all the polluted run-off in the Los Angeles area would take 20,000 such plants.
"It's just putting a Band-Aid on a hopelessly big cut," Mr Hoskinson said. Meanwhile, the surfers are being rapidly outnumbered by inline skaters and bikers on the beach path -sun worshippers who make sure they stay firmly on dry land.