Brown water advisory issued for Hilo Bay, Hāmākua Coast

Brown water along Hilo Bay and the Hāmākua Coast carried a public-health warning Monday, with the Hawaii Department of Health telling beach users to stay out of water that looked brown, turbid or cloudy. The advisory is aimed squarely at swimmers, waders, paddlers and families headed to the shoreline after heavy rain, when runoff can wash sediment, debris and contaminants into nearshore waters.

The Clean Water Branch says a brown water advisory is issued when water may contain land-based polluted runoff. That runoff can carry pathogens and other pollutants from cesspools, septic tanks, animal feces in storm drains, overflowing manholes and polluted discharges from commercial or industrial sites. The state’s guidance recommends staying out of brown water for 48 to 72 hours after heavy rain, and it says to wait for further Department of Health direction before getting back in.

For Hawaii Island, the warning has added weight because Hilo Bay and the Hāmākua Coast are heavily used for recreation and cultural activity. Rain can quickly send murky water from roads, yards, streams and drainage systems into the ocean, turning familiar shoreline areas into places where direct contact is risky even before water is formally sampled. The department also issues brown water advisories when heavy rain falls or when a Flash Flood Warning has been issued, conditions that can rapidly push surface runoff into the sea.

This was not the first alert for the same stretch of coast. The state’s Environmental Health Portal showed a brown water advisory for Hilo Bay and the Hāmākua Coast posted on April 30, 2026, underscoring how often rain-driven runoff can affect the corridor around Hilo town and Hilo Harbor.

Local research helps explain why the warning matters. University of Hawaii at Hilo scientists have found that rainfall-driven runoff increases harmful bacteria in Hilo Bay, and that cloudy water is associated with higher bacteria concentrations. A 2024 technical report for Hawaii County’s Department of Public Works said Hilo Bay is designated as an impaired body of water under state and federal water-quality standards and is highly susceptible to brown water.

That report also said the Hilo Harbor breakwater interferes with circulation and can prolong brown-water conditions in the bay. In other words, the murky water can linger after the rain stops, especially in a bay where built structures slow the flushing of runoff out to sea. Federal planning work has also examined whether changing the breakwater could improve circulation and water quality, a sign that this is not just a temporary nuisance but a recurring public-health issue tied to the bay’s design.