On Oahu’s North Shore, the generally flat seas of summer are ideal for snorkeling, swimming and tide-pooling at places like Sharks Cove in Pupukea that are dangerous during winter’s big waves. But there can be other, microscopic threats in water, namely bacteria and other microorganisms that can cause illnesses such as gastroenteritis.

“We (almost) never do tide pools for that exact reason! It’s just basically bathing in bacteria,” said Pupukea resident Tiffany Foyle, whose 6-year-old son, Bear, loves the ocean. Due to “the amount of dog pee and poop that collect in the sand, plus just general (staphylococcus bacteria) and human waste” that can be present, she waits as a rule for standing water in tide pools to be washed out by the ocean and refilled with fresh water before going in.

Indeed, on Sunday at Pupukea Tidepools, Surfrider Foundation volunteers collected water samples that were revealed by lab tests to contain high levels of enterococci, a bacteria which indicates fecal pathogens also may be present, said Christina Comfort, an oceanographic research specialist at the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa. Enterococci levels were at 235 per 100 milliliters of water, which is above the 130-per-milliliter threshold for high contamination, triggering warning advisories, used by the Clean Water Branch of the state Department of Health.

Comfort co-supervises a team of volunteers, herself included, who test waters at 20 beaches around Oahu for Surfrider Foundation’s Blue Water Task Force.

“It’s citizen science,” she said. “We test on Sundays because that’s the one day we all don’t work.” The testing is done at the Hawaii Pacific University marine science lab, where the volunteers are trained, she added. Other sites tested Sunday with moderate enterococci levels included Chocolates at Haleiwa (120/100 ml.), Kuliouou Stream (60/100 ml.) and Magic Island Canoe Launch (81/100 ml.). Samples from Magic Island Bowls and Velzyland, among others, had levels of zero. Oahu test locations and results can be viewed at surfrider.org/blue-water-task-force/chapter/44.

Surfrider reorganized its beach-water testing program in February 2018 with the goal of adding frequency and new sites to the water quality monitoring already being done by DOH, Comfort said.

“We prioritize beaches into tier levels,” said Myron Honda, supervisor of the monitoring and analysis section of the DOH’s CWB. “Tier 1 beaches, including Waikiki, Ala Moana and Hanauma Bay, the most frequently used by the highest number of users, are tested once a week.” Tier 2, including Bellows, Kalama, Punaluu and Hauula beaches, is tested biweekly to monthly.

Honda urged people to visit CWB’s website at eha-cloud.doh.hawaii.gov/cwb to find advisories about brown water, sewage spills or high bacteria levels, and sign up for email alerts. Members of the public can call CWB at 586-4309 to report possible contamination. He noted that turtle excrement, which stays intact for long periods in the water, is often mistaken for the human variety, which breaks up within hours.

While CWB doesn’t test for staphylococcus bacteria, Honda recommended that people avoid very crowded, calm waters at places like Pokai Bay in Waianae that lack circulation. They should be avoided because the bacteria wash off some people’s skin and nasal passages and can collect and cause infections, Honda said. This also can happen in tide pools, “where water just stagnates and a lot of people go in,” he added.