On July 15, during the latest big swell in this epic South Shore summer, Oahu native Fred Farmer went surfing at Publics, a long, left-breaking wave that peels over the shallow reef off Public Bath Beach in Waikiki.

Two days later, on Wednesday, he came down with the runs, fever, weakness and exhaustion: symptoms and timing consistent with gastroenteritis, the most common illness linked to swimming in sewage-­polluted water, according to the U.S.Environmental Protection Agency.

Still sick the next day, Farmer read in the Honolulu Star-Advertiser that a high-bacteria advisory for Public Bath Beach had been posted Wednesday: Routine water sampling by the state Department of Health Clean Water Branch had found 384 enterococcus bacteria per milliliter; the advisory threshold is 130 bacteria. Enterococcus is an indicator bacterium found in the presence of fecal pathogens that can cause gastroenteritis as well as eye, nose and ear infections.

“I’m pretty sure I got sick with gastroenteritis from surfing Publics,” said the 60-year-old engineer.

The Health Department doesn’t track the incidence of waterborne illness among Hawaii swimmers, but as anyone who’s contracted a stomach upset or sinus infection after ocean activities can guess, Farmer is far from alone.

Now some numbers confirm he’s got lots of company: A new water pollution report, “Safe for Swimming? Water Quality at Our Beaches,” scheduled for release today by the national nonprofit Environment America Research & Policy Center, says an estimated 57 million people get sick from recreational waterborne illnesses each year. After reviewing data of beach closures and advisories in 29 U.S. coastal and Great Lakes states and Puerto Rico, the group found that 2,627 out of 4,523 sites — nearly 60% of all beaches tested — had above-threshold levels of fecal contamination on at least one day in 2018.

And while the state Clean Water Branch’s website states that gastroenteritis can also be caused by food poisoning, citing beach picnics left out too long in the sun, those who get wet get sick more often than those who stay dry, according to the journal Environmental Health. “Water recreators have a higher incidence of acute gastrointestinal illness (AGI) and non-enteric illnesses, including respiratory, ear, eye, and skin symptoms than non-­water recreators,” the journal reported in a 2018 analysis of illness contracted during water recreation.

According to the Environment America report, 90 of 218 beach sites sampled in Hawaii, or 41%, were potentially unsafe for swimming for at least one day in 2018, according to the report, which compiled and analyzed data collected by EPA from states, territories and tribal governments required to monitor recreational waters under the federal Beach Act, which provides some funding for that purpose.

The sampling site at Keehi Lagoon North on Oahu was potentially unsafe for 11 out of 91 sampling days, more than any other site in the state, followed by Keehi Lagoon South at 10 days, the report found.

Among Hawaii counties, Kauai had the highest average percentage of sampling days finding potentially unsafe water, at 13%. In Honolulu County bacterial levels exceeded the EPA standard on 8% of testing days; Maui County came in at 5% and Hawaii County at 4%.

Among Oahu beaches, Punaluu Beach Park had potentially unsafe waters on nine, or 75%, of its 12 sampling days; Hanauma Beach Park on six, or 16%, of 37 days; Waimanalo Beach on four, or 11%, of 36 days; West Sand Island Park on seven, or 8%, of 91 days; and Kakaako Park on four, or 11%, of 91 days.

In California, 466 of 584 beach sites were potentially unsafe for at least one day.

“Forty-seven years ago, when Congress passed the Clean Water Act, one of its key goals was to make all of our waterways safe for swimming,” said John Rumpler, co-author of the Environment America report. “Clearly we’re not reaching that goal, and the millions of Americans going to the beach this summer are probably not aware of the scope of the problem.”

Farmer, whose symptoms persisted until Saturday, a day after the advisory was called off, said that he is now all too aware of the risk.

The report can be viewed at environmentamericacenter.org.