Management plan of polluted Hilo Bay watershed moving forward with $2 million federal grant

Hilo Bay is the state’s largest watershed, covering about 470 square miles from the summits of Mauna Kea and Mauna Loa to the sea. But for decades, polluted rain runoff, untreated sewage in groundwater and other factors have led to poor water quality in the bay and its sub-watersheds, negatively impacting endangered habitats and local communities.

Hawaiʻi County also has tried to work on the problem for decades but was held back by a lack of data. Now, the county is continuing its efforts to find a watershed solution, with a $2 million grant from the National Fish and Wildlife Foundation, with funding from the Department of Defense, that was awarded in 2024.

The county’s Department of Research and Development will use the funding to complete the Hilo Bay Resilience and Watershed Management Plan, which will guide infrastructure and resilience efforts to conserve the biodiversity of East Hawaiʻi and restore water quality.

To gather public input, the county and Lynker Corp., a science and technology company that will develop the plan, hosted a Community Listening Fair on Saturday at the Aupuni Center in Hilo.

“This is an important, first-level step with the community,” said Chris Hawkins, a coastal social scientist with Lynker. “The last thing we want to do is come into this project with preconceived notions.

“We want to hear from the community on what the watershed means to them. People who were born here on Hawaiʻi look at the watershed differently with more cultural importance. What does the community value, what are things they are concerned about, or things they want to see years from now?”

Throughout the day, nearly 200 people talked about their concerns and ideas with people working on the watershed plan. They were invited to write concerns and ideas onto sticky notes and place them on maps of the watershed near the relevant area.

Some recurring ideas included:

• Prioritizing cesspool conversions
• Enforcing and subsidizing septic systems
• Researching sewage settling ponds
• Planting mangrove trees to create an estuary environment
• Testing water quality more frequently
• Stopping all use of herbicide

About 69% of the Hilo Bay watershed is state-owned and encompasses agricultural, forest, conservation, urban and rural lands. It receives between 75 and 300 inches of rainfall annually, which often causes runoff from groundwater and soil that contain pollutants.

In 2005, the University of Hawaiʻi and the Hilo Bay Advisory Group created a 195-page restoration plan identifying pollutants, data gaps and many recommendations to improve the water quality. But the plan could not move forward due to insufficient data, the county said on its Hilo Bay website page.

The U.S. Army Corps of Engineers said additional technical studies, including water quality monitoring, was needed to complete “a data-informed Watershed Management Plan.” 

Since 2005, many organizations, and especially the University of Hawaiʻi at Hilo, have continued to contribute to data reporting on Hilo Bay and the watershed.

In 2023, the U.S. Army Corps of Engineers recommended comprehensive water quality and sediment analysis, mapping sediment sources, and developing a watershed management plan with prioritized strategies and funding pathways.

The county hired Virginia-based Lynker Corp., which has expertise in watershed and coastal management strategies, to compile available data and to identify data gaps needed to complete the technical studies needed for a management plan.

Three of Lynker’s subcontractors completed the draft for discussion and review by the county and a Community Advisory Committee.

The committee is composed of community members, nonprofit organizations, educational institutions and government agencies that will provide advisory guidance to the Department of Research and Development, other parts of the county, and the planning team throughout the project. People can still join the committee. Click here for a sign-up form.

Lynker will create a new plan that integrates Army Corps recommendations and the requirements of the Environmental Protection Agency.

“Truthfully we are standing on the shoulders of the giants who spent time researching and creating a plan that was, unfortunately, not compliant with the Environmental Protection Agency,” Hawkins said. “They needed more data and research done on where pollutants come from, which is where we start to come in.”

According to Lynker’s draft of the data gap analysis, the pollution to Hilo Bay has two primary sources — untreated sewage in groundwater that leaches through highly porous volcanic rock, and sediment and other contaminants from agricultural or urban surfaces through high-intensity rainfall, overland flow and flooding.

The plan will consider and prioritize all recommended restoration activities, with special emphasis on nature-based solutions, cultural knowledge, coastal resilience and habitat protection, according to the Department of Research and Development.

“Community outreach is the first step because many of them want to be part of the solution,” said Stacey Kilarski, project manager with Lynker. “They want to learn more, share their experiences and opinions, and state their goals and visions.

“After we summarize what we’ve gathered here today, we will synthesize this data with our previous data collection and bring it to a Community Advisory Committee, which will help guide the next steps.”

And there will be many more steps in a process that will not result in a final management plan until the fall of 2027.

With climate change and population growth, the Hilo Bay watershed has become an even more pressing issue to be addressed. The plan will help guide the county toward more sustainable infrastructure and resilience efforts.

“The trajectory of climate change and the possibility of a super El Niño means the issues in Hilo Bay will only be exacerbated,” Hawkins said. “You cannot afford to wait, and community members have waited long enough.”

“There are layers of problems that need to be addressed,” KIlarski said. “And, we have the opportunity to do something.”