Is Hawaii's Beach Water Getting Cleaner or Dirtier?

Two main drivers of Hawaii beach water-quality variability year-over-year:

1. Storm cycles. Kona Lows and major rain seasons drive Brown Water Advisories. The 2026 Kona Low cycle in March–April was unusually persistent and pushed Hawaii's BWA count up. Sewage spills correlate with rainfall (overwhelmed WWTPs and cesspool seepage during storms).
2. Infrastructure events. Isolated events at specific facilities (Wahiawa WWTP, Waimea WWTP, Lahaina post-fire) can move the annual count significantly. Aging wastewater infrastructure across the state is a continuous risk factor.

Underlying structural factors (88,000 active cesspools, urban runoff, agricultural drainage) remain stable year-over-year and produce a consistent baseline. The state's 2050 cesspool-conversion mandate may eventually reduce this baseline, but the deadline is decades out.

Data is pulled fresh from the Hawaii DOH Clean Water Branch event API on every page rebuild. We compare the last 365 days (rolling) to the prior 365 days. "Events" = each Beach Advisory, Brown Water Advisory, or Sewage Spill issued by DOH. "Advisory-days" = cumulative open-day count across all events that overlap the window. Per-island assignment uses the DOH "Island" field; statewide events count under each island they reference.

Limitations: DOH testing coverage is uneven across the state (47 stations across the 4 main islands; 0 on Molokaʻi/Lanaʻi). An "advisory-day" reflects what DOH posted, not the underlying water quality at every Hawaii beach. We publish Surfrider BWTF community-tested data for Oʻahu, Maui, and Kauaʻi, while naming the Molokaʻi/Lānaʻi gap separately.