School’s out, the days are long, and it’s time to hit the beach, splash in the surf or snorkel over the reefs. But beware: two beaches on Oʻahu and Kauaʻi topped the list of shorelines across the country that are top-priority “bacteria hot spots,” according to a new report by the Surfrider Foundation.

More than 90% of the water samples collected in 2024 from the popular swim spots — Kahaluʻu on Oʻahu and Waikomo Stream at Kōloa Landing on Kauaʻi — had bacteria levels above state health standards. While other parts of the state’s coastlines are even more polluted, of places used by the public, these spots are among the highest-risk for poor water quality.

The data comes from the foundation’s Blue Water Task Force, which analyzes water quality where local governments typically aren’t keeping track. Nationally, 80% of test sites last year had at least one high bacteria result above state health standards. 

“Each location regularly shows dangerous levels of fecal-indicator bacteria tied to human illnesses, including gastrointestinal issues, flu-like symptoms, and serious skin conditions like MRSA and staph infections,” the report said.

Hawaiʻi’s reliance on cesspools has led to particularly stark problems. Wastewater contributes to the problem at Kahaluʻu, according to Daniel Amato, who coordinates the foundation’s data collection on Oʻahu. 

“It’s one of the areas that is just kind of chronically polluted with fecal indicator bacteria,” he said.

Hawaiʻi’s Hot Spots

About a fifth of Surfrider’s 83 test sites in Hawaiʻi had high levels of bacteria more than half of the time, mostly in locations near cesspools. 

In some places, it was even worse. 

Bacteria was detected in every sample collected from Nāwiliwili Stream, which feeds into Kalapaki Bay at Nāwiliwili Beach Park on Kauaʻi. The site has failed to meet water quality standards every month since 2018. 

Just last year, a sign finally went up warning would-be swimmers that high bacteria levels had been detected in the stream, after almost a decade of pressure from Surfrider Foundation. 

Other places also consistently had excessively high bacteria levels. On Oʻahu, Surfrider’s team collects samples across the island every two weeks. One site on Oʻahu’s Windward side, Punaluʻu Beach Park, fell short of state health standards in every sample collected last year.

The problem is particularly bad at the mouths of streams where water flows out to the ocean. Those fresh water sources dump runoff from cesspools, animal waste and other sources of bacterial pollution into the ocean.  

“The bacteria is coming down through these watersheds. It’s being generated by feral animals and human on-site wastewater systems like cesspools and septic tanks, particularly after heavy rains and brown water type events,” Amato said. “So that’s our primary concern — stream mouths near the ocean, where families and people tend to be in the water.”

Maui’s Waters Among Cleanest

In January 2024, several months after the devastating wildfire in Lahaina, Surfrider tested samples from nearby sites for evidence of fire-related contaminants. And here’s some good news: The tests turned up no evidence of any risk to human health from contamination after the fire.

Actually, Maui’s waters tend to be among the cleanest. More than 50% of spots where Surfrider collected samples last year never saw high levels of bacteria in excess of health standards. And even when there were indications of high bacteria levels, those spikes were less frequent on Maui than on Oʻahu and Kauaʻi. 

So what’s safe? 

Beaches that don’t have freshwater sources like streams tend to have less bacteria. 

During the rainy season, “storms serve to ‘flush’ the islands and can result in large amounts of water, sediment, wastewater, and pollutants flowing downhill into the ocean,” bringing with them more bacteria, according to the report. 

But water quality issues and bacteria spikes don’t just happen in the winter. Stagnant water also leads to higher bacteria levels. 

Surfrider recommends paying attention to water quality conditions, avoiding brown water even if there’s no posted warning and staying out of those spots where fresh water streams flow into the ocean.

“For me, it’s more about areas where families go. You always see kids playing in the streams, and you have the beach parks,” Amato said. “And our data is telling us that is not a good idea.”

 “If the water looks questionable,” he said, “it probably is.”

Civil Beat’s community health coverage is supported by the Atherton Family Foundation.

Civil Beat’s coverage of climate change and the environment is supported by The Healy Foundation, the Marisla Fund of the Hawaiʻi Community Foundation and the Frost Family Foundation.