Where Are You
Getting In Today?
Find the clearest beaches, swim spots, and dive sites near you — ranked by real-time water clarity.
How Water Clarity Is Scored
Every score is a live calculation from real weather, marine, and advisory data. The base score is a weighted sum of six factors. Alerts and community reports adjust it from there.
The score is a forecast — not a photograph.
WCS forecasts water clarity from live weather, wave, and advisory data. But no model can see the plankton bloom, the brown-water plume, or the patch of glass a swimmer actually encounters in real time. That's where eyes-on community reports come in.
Reports from the last 24 hours show as a second circle next to the algorithm score — recent reports weighted more heavily. When the two disagree, trust the eyes-on reports. Fresh reports from real swimmers beat any model. And if you just got out of the water — share what you saw. You help the next swimmer know what they're walking into.
The Six Weighted Factors
Rainfall & Runoff
The #1 driver of murky water. We track current precipitation plus a 72-hour antecedent decay kernel — a storm 2 days ago still penalizes the score because watershed sediment lingers. Beaches near stream mouths get an extra penalty.
Weight: 30%Wind Speed
Strong winds stir bottom sediment and create surface chop. A 30 mph wind drops this factor to zero; glassy conditions max it out.
Weight: 20%Wave Height (Direction-Aware)
Big waves churn sediment. We multiply wave height by the beach's exposure to the incoming swell — a 12ft north swell doesn't tank a south-facing beach's score, but an 8ft swell hitting head-on will.
Weight: 20%Sun & Cloud Cover
Sunlight lets swimmers perceive depth and color underwater. Cloud cover reduces apparent clarity. We also adjust for local solar time — predawn and dusk scores drop even in perfect water.
Weight: 10%Wave Period (Direction-Aware)
Longer periods mean cleaner groundswells. A 16-second period reaches the seafloor and churns sediment on exposed coasts — but not on shadowed ones. Period is weighted by the same directional exposure as wave height.
Weight: 10%Ocean Currents
Strong currents drag sediment through the water column. Reef-protected bays with weak currents score higher than exposed points with fast-moving water.
Weight: 10%On Top of the Base Score
NWS Alert Penalties
Flash Flood, High Surf, Small Craft, Wind Advisory, Tsunami — these subtract points (up to -50 for Tsunami, -45 Flash Flood, -30 High Surf). Active for US beaches only (Hawaii, California, Florida). Lingering penalties apply for 24-48 hours after alerts expire.
SubtractiveBrown Water Advisory Floor
Hawaii DOH's 48-72hr post-storm advisory caps the score at 25 regardless of other factors. Driven by explicit NWS alerts or inferred from Hawaii + flood alert + heavy antecedent rainfall. Pathogen and visibility guidance.
Hard CapHawaii METAR & NWS Override
Open-Meteo's worldwide data is too coarse for Hawaii's microclimates. We fetch ground-truth cloud observations from 9 airport METAR stations and use NWS HRRR-HI 2.5km forecasts for 40 terrain-blocked beaches where the airport's weather doesn't represent what the beach sees.
Hawaii OnlyKnown Limitations
Open-Meteo underestimates rainfall in Hawaii's microclimate — our Brown Water Advisory and antecedent penalties are designed to partially compensate, but real-world conditions can deviate. International beaches don't get NWS alerts (outside US coverage). The score is a live forecast, not a guarantee. Always check the ocean before you enter it — and when possible, check recent eyes-on reports too.