Year-over-year DOH data: in the last 365 days, Hawaii recorded 130 water-quality events (1,640 cumulative advisory-days) versus 56 events (628 advisory-days) the prior year. Statewide trend: getting dirtier (+161.1% in advisory-days).
| Island | Prior 365d | Last 365d | Change |
|---|---|---|---|
| Oʻahu | 22 | 60 | +172.7% |
| Maui | 14 | 23 | +64.3% |
| Hawai‘i (Big Island) | 12 | 21 | +75.0% |
| Kaua‘i | 8 | 24 | +200.0% |
| Event Type | Prior 365d | Last 365d | Change |
|---|---|---|---|
| Beach Advisory | 14 | 21 | +50.0% |
| Brown Water Advisory | 30 | 92 | +206.7% |
| Sewage Spill | 12 | 17 | +41.7% |
Two main drivers of Hawaii beach water-quality variability year-over-year:
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: Hawaii DOH's September 2024 Beach Monitoring Program document lists about 407 BEACH Act beaches statewide and reports that about 167 were monitored in 2023; frequency varies by tier and resources. Molokaʻi and Lānaʻi are not routinely monitored. 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.