Several coastal areas in Hawaii are under a brown water advisory after high surf reached roadways, potentially bringing animal feces, pesticides, pathogens and a brew of other unwanted debris into the islands’ normally pristine ocean, according to Hawaii’s Clean Water Branch division of the Department of Health. Multiple advisories were issued for the island of Maui, for the North Shore and West Maui areas, as well as for destinations on Oahu and Hawaii Island. 

The warnings come amid a high surf advisory that’s slated to last until 6 a.m. local time Friday, the National Weather Service’s website shows. Waves are expected to reach as high as 35 feet along north-facing shores, according to a Dec. 28 high surf warning, and they’re expected to rise even higher until Friday morning. As long as the brown water advisory is in effect, residents are urged to stay out of the ocean, which could be contaminated by overflow from cesspools and septic tanks, according to Clean Water Branch’s site. 

The department did not respond to SFGATE’s questions by the time of publication. 

Black Rock, one of the areas on Maui on alert for brown water, is normally a snorkeling destination and site for cliff-diving ceremonies. Meanwhile, on Oahu, Kaena Point State Park, a popular area for hiking, picnicking and sightseeing opportunities, is facing flooded roads. Yokohama Bay, another region under the brown water advisory, was previously described by Hawaiian Airlines as “isolated and tranquil.” 

“This time of year produces incredible surf,” Shayne Enright, a Honolulu Ocean Safety spokesperson, previously told the Associated Press, “but it can also be very dangerous.”