Nearly 55 million gallons of sewage are threatening Hawaii's coral reefs, with much of the pollution seeping into the ground daily just a few hundred yards from the coast and the 410,000 acres of reefs beyond. The contamination exposes reefs to bacteria, viruses, and nutrients that promote the growth of smothering algae, adding to existing pressures from climate change, ocean acidification, and plastic and agricultural pollution.
Researchers have now determined the scale of the threat, identifying contaminated locations and showing that sewage-affected groundwater is reaching some of West Hawaii Island's most vulnerable reefs. More than 40 percent of dozens of sites tested along 120 miles of coastline were found to be contaminated, according to a study led by Arizona State University.
Kelly Hondula, an associate research scientist at Arizona State University, said the findings were concerning but unsurprising. Her team used helicopter-mounted sensors and cameras, field sampling, and statistical models to trace high levels of faecal bacteria. In 42 percent of the 47 sampled sites, elevated levels of Enterococcus were detected, with 23 percent exceeding human health risk thresholds. Exposure to sewage-polluted water can cause viral, parasitic, and bacterial infections, leading to gastrointestinal and immune system problems.
The study identified inland sewage systems and coastal urban development as key predictors of contamination. The South Kona region, famed for its coffee and located 10 miles south of Kailua-Kona on the Big Island's west side, was especially vulnerable due to intensive coastal development and its volcanic terrain, which allows sewage to travel rapidly through underground water systems. The area includes Kealakekua Bay State Historical Park, home to green sea turtles and tropical fish, while Hawaii's reefs support over 7,000 known marine species.
Researchers recommend monitoring the health of affected areas, mitigating sewage pollution, and implementing new green infrastructure and wastewater treatment systems. Greg Asner, professor and director of the ʻĀkoʻakoʻa Reef Restoration Program, stressed that restoration goes beyond planting corals, encompassing land management, reef interventions, and education efforts.
