Okinawa 3-Area Dive Comparison: Yonaguni, Ishigaki & Kerama — 7,800 Real Observations

Okinawa's Ocean Is Not Uniform

People say 'Okinawa has clear water,' but the numbers differ significantly between Yonaguni, Ishigaki, and Kerama. Yonaguni's annual average of 24.5m is Japan's top-ranked dive area. Ishigaki averages 20.5m and Kerama 19.4m — more than a 5m difference within 'Okinawa.' Using 7,845 real observations, we compare visibility, water temperature, and seasonal patterns across all three areas.

3-Area Summary Comparison

※Best value in bold blue

Monthly Visibility (All 12 Months)

Color: ≥25m deep blue, ≥22m blue, ≥20m light blue, ≥18m pale cyan

Remarkable Finding: Yonaguni's Worst Month Beats Others' Best

Yonaguni's worst month — January at 22.4m — exceeds Ishigaki's best month (March, 21.9m) and Kerama's best month (July, 21.3m). In other words, Yonaguni surpasses the peak levels of the other two areas every single month of the year. Where does this extraordinary advantage come from?

The main reason is geographic position and the Kuroshio current. Yonaguni is Japan's westernmost island, and the Kuroshio main stream flows directly past it. This warm, nutrient-poor oceanic water is constantly supplied to the coast, keeping plankton density low and visibility high. In contrast, Ishigaki and Kerama are more influenced by surrounding land and reefs, with greater runoff from rainfall and rivers.

Seasonal Visibility Summary

Key Characteristics & Best Times

Yonaguni: Japan's Premier Open-Ocean Visibility

Autumn (Sep–Nov) delivers the best clarity, with September averaging a remarkable 27.3m. The hammerhead shark season (Jan–Mar at 22–24m) is also highly popular. Strong currents are common, making many dives intermediate to advanced level. The AI visibility prediction R² of just 0.046 reflects how highly variable daily conditions can be.

Ishigaki: Spring Peak, Consistent Year-Round Diving

The monthly peak is March at 21.9m. Visibility is best before the rainy season (March–May), and remains at 20–21m through summer (June–August). With the smallest seasonal range of the three areas (2.8m), Ishigaki offers consistent diving year-round. Combined with the vast Sekisei Lagoon coral reef ecosystem, it excels in both clarity and marine biodiversity.

Kerama: Day-Trip Destination from Naha

Just 35 minutes from Naha by jet foil, Kerama offers unmatched accessibility. Annual average of 19.4m is the lowest of the three, but July reaches 21.3m. 'Kerama Blue' — a distinctive deep azure clarity — is popular with tourists and casual snorkelers. High sea turtle encounter rates (especially near Zamami Island) make it ideal for family diving. For those prioritizing convenience and marine life encounters over maximum visibility, Kerama is the best choice.

Which Area Should You Choose?

Summary

Yonaguni, Ishigaki, and Kerama all rank among Japan's clearest dive areas, but their strengths differ significantly. Yonaguni is for advanced divers seeking 'otherworldly clarity.' Ishigaki excels for those wanting both reef diversity and high visibility. Kerama is ideal for those who want to enjoy Okinawa's waters conveniently and casually. The best choice depends on your priorities — but any of the three will deliver world-class diving.

Data source: scraped from public dive logs. Yonaguni: 4,826 obs; Ishigaki: 1,473 obs; Kerama: 1,546 obs.