According to a recent study by researchers at the University of Hawaii, the water quality in Hilo Bay will only worsen as climate change increases.

The study, published earlier this year in the journal Water Environment Research, found that freshwater discharges into Hilo Bay are associated with high concentrations of harmful bacteria, and that these concentrations are likely to increase as sea levels rise and extreme weather events become more frequent.

According to the study, certain parts of Hilo Bay contain pathogens such as Staphylococcus aureus (commonly called staph) at concentrations that range from six to 78 times higher than baseline. These high concentrations are associated with lower tidal heights, higher freshwater runoff and the density of nearby sewage disposal systems – i.e. cesspools.

“There are many factors,” said study co-author and UH Hilo professor Tracy Wiegner. “There is a huge concentration of cesspools in the area, all on lava rock, which is very porous and permeable.”

Wiegner said sewage from a cesspool in Keaukaha could seep into the bay within hours to days.

Steven Colbert, associate professor of marine sciences at UH-Hilo, said similar conditions are occurring throughout the east and south coasts of the Big Island.

“A lot of the island is just too young to have the soil for functioning septic tanks,” Colbert said. “Instead, we have all these cracks and fissures and lava tubes underneath us that the sewage just flows through.”

As sea levels rise, sewage will flow into the sea even faster and more cesspools will be flooded, Colbert said. At the same time, as the ocean warms, Hilo Bay will become a better habitat for bacteria.

Although water quality in the bay has long been known to pose a health risk, Colbert said the study at least helped confirm the origin of the pathogens.

“(To fix the problem) you will need very expensive resources,” Wiegner said. “That’s why the reconstruction of the cesspool took so long.”

“Ideally, we would connect the homes in Keaukaha to a sewer system and then bring the Hilo wastewater treatment plant back to its maximum capacity…or even more,” Wiegner continued.

But the question of who will bear the cost of such a conversion remains open. Wiegner said it is clear that Keaukaha already bears the brunt of sewage pollution from the bay and most residents cannot afford to convert their septic tanks themselves.

A study commissioned by Hawaii County could find some solutions, but not for two years. In 2023, the county’s Department of Research and Development applied for federal funding for a comprehensive study of the Hilo watershed.

In March, the National Fish and Wildlife Foundation awarded the county $2 million for the study, and the agreement between the county and the NFWF was officially signed Tuesday.

Beth Dykstra, economic development specialist for research and development, acknowledged that the project is moving slowly due to the bureaucratic hurdles that come with federal funding, but said the two-year study should bear fruit by the end of 2026.

This study, Dykstra said, would essentially build on the UH study and other research, but would be conducted on a larger scale across the entire watershed.

The study will also include potential solutions and, importantly, possible sources of funding.

“That’s what this study is really about,” Dykstra said. “So that we can seek funding.”

Dykstra said that while the Hilo watershed is the largest in the state, neither the county nor the state health department have sufficient resources to protect its ecology. In addition, Hilo’s ailing wastewater treatment plant is on its last legs and will cost about $300 million to renovate.

Despite the problems, the condition of the catchment area is not yet too bad, according to Colbert.

“It doesn’t stop me from swimming,” Colbert said. “I just have to be careful. I shower afterward, and if I have an open wound, I probably don’t go in. If the water is brown after a storm, you probably shouldn’t go in.”