Japan's Top 10 Most Stable Dive Sites: Clear Water Year-Round
2026-03-11
"Great visibility any time of year" — the ideal every diver seeks. Underwater visibility fluctuates with phytoplankton cycles, thermocline formation, spring turbidity, and typhoons. Yet some Japanese dive sites maintain remarkably consistent clarity throughout the year.
Using 46,000+ real observations (2015–2026), we calculated the difference between each site's best and worst monthly average visibility — ranking the 10 sites with the smallest seasonal swing. "High visibility" and "stable visibility" don't always go hand in hand.
Top 10 Most Stable Dive Sites by Seasonal Range
| Rank | Site | Annual Avg | Seasonal Range | Worst Month | Best Month | Observations |
|---|---|---|---|---|---|---|
| 1 | Akinohama (Izu Oshima) Izu Oshima, Tokyo | 14.7m | 1.9m | 13.6m (5月) | 15.5m (9月) | 1,309 |
| 2 | Ishigaki Island Okinawa | 20.6m | 2.6m | 19.4m (12月) | 22m (3月) | 1,473 |
| 3 | Kerama Islands Kerama, Okinawa | 19.6m | 3.3m | 18.3m (1月) | 21.6m (7月) | 1,546 |
| 4 | Shirahama Shirahama, Wakayama | 15.3m | 3.3m | 13.5m (9月) | 16.8m (1月) | 616 |
| 5 | Osezaki Outer Ocean Osezaki, Shizuoka | 11.7m | 3.4m | 9.9m (4月) | 13.3m (1月) | 931 |
| 6 | Omijima Omijima, Yamaguchi | 10.6m | 3.4m | 8.7m (10月) | 12.1m (1月) | 2,095 |
| 7 | Osezaki Cape Osezaki, Shizuoka | 11.5m | 3.7m | 10.2m (4月) | 13.9m (2月) | 434 |
| 8 | Futone Tago, Shizuoka | 14m | 4m | 11.7m (5月) | 15.7m (1月) | 934 |
| 9 | Yonaguni Island Yonaguni, Okinawa | 25.4m | 4.6m | 23.5m (1月) | 28.1m (9月) | 4,826 |
| 10 | Kushimoto Kushimoto, Wakayama | 13.4m | 4.2m | 10.9m (1月) | 15.1m (2月) | 3,169 |
Monthly Visibility Heatmap
| Site | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 秋の浜 | 15.2 | 15 | 14.2 | 13.8 | 13.6 | 14.9 | 14.8 | 14.4 | 15.5 | 15.2 | 14.8 | 15.2 |
| 石垣島 | 20.9 | — | 22 | 21.3 | 20.4 | 20.2 | 20.9 | 21 | 21.5 | 19.7 | 19.7 | 19.4 |
| 慶良間 | 18.3 | 18.3 | 19.2 | 18.8 | 19.8 | 20 | 21.6 | 21.1 | 19.9 | 19.3 | 19.3 | 18.7 |
| 白浜 | 16.8 | 14.8 | 15 | 16.4 | 15.2 | 16.4 | 14.9 | 15.4 | 13.5 | 14.8 | 13.6 | 14.8 |
| 大瀬崎外海 | 13.1 | 12.9 | 11.4 | 9.9 | 11.2 | 12.6 | 10.6 | 12.3 | 12.8 | 10.5 | 10.7 | 13.3 |
| 青海島 | 12.1 | 10.1 | 11.1 | 9.9 | 10.2 | 10.8 | 12 | 12 | 9.7 | 8.7 | 9.9 | 10.6 |
| 大瀬崎先端 | 13.8 | 13.9 | 11 | 10.2 | 13.2 | 11.8 | 10.7 | 10.7 | 10.7 | 11 | 10.6 | 13.8 |
| フトネ | 15.7 | 15.1 | 13.3 | 13.2 | 11.7 | 13.9 | 13.3 | 13.3 | 15.2 | 14.6 | 13.6 | 14.3 |
| 与那国 | 23.5 | 24 | 24.9 | 25 | 25.3 | 25.3 | 26.4 | 27.4 | 28.1 | 27.5 | 25.1 | 24.1 |
| 串本 | 10.9 | 15.1 | 13.4 | 12.3 | 13.2 | 14.1 | 14.5 | 12.8 | 13.4 | 14.8 | 12.9 | 12.5 |
#1: Akinohama (Izu Oshima) — Only 1.9m Annual Range
Izu Oshima's Akinohama beach is Japan's most consistent dive site, with a remarkable 1.9m range between its worst month (May, 13.6m) and best month (September, 15.5m). All 1,309 observations show that no matter when you visit, you'll get at least 13.6m of visibility on average.
The stability stems from its island geography. Isolated from mainland coastal runoff, Kuroshio oceanic water dominates year-round, suppressing phytoplankton blooms. Interestingly, this uniqueness also makes it one of the hardest sites for our AI to predict (R² is negative for the general model).
#2: Ishigaki Island — 20.6m Average with Just 2.6m Swing
Ishigaki combines high absolute visibility (20.6m annual average) with outstanding stability (2.6m range). Even in its worst month (December, 19.4m), you're still looking at nearly 20 meters of clarity. The Kuroshio Current and pristine coral reef environment maintain this consistency.
#3: Kerama Islands — The Original "Kerama Blue"
The Kerama Islands coined the term "Kerama Blue" for good reason. At 19.6m average with a 3.3m swing, even January (the worst month at 18.3m) delivers exceptional visibility. Based on 1,546 observations, this is one of Japan's most reliable high-visibility destinations.
What Makes a Site Stable?
Analyzing the Top 10 reveals common traits:
- Island/offshore location: Akinohama, Ishigaki, Kerama, and Yonaguni all sit away from mainland nutrient runoff
- Kuroshio influence: Kushimoto and Kannoura receive constant oceanic water that dilutes seasonal turbidity
- Oligotrophic waters: Low-nutrient environments suppress phytoplankton blooms that drive seasonal visibility drops
Stability vs. High Visibility: Not the Same Thing
Note that Yonaguni ranks 9th despite having Japan's highest average visibility (25.4m). Its 4.6m swing (23.5–28.1m) is larger than Akinohama's 1.9m. If your goal is "at least X meters every single month," Akinohama, Ishigaki, and Kerama outperform Yonaguni on consistency.
Omijima (Yamaguchi, #6) is another surprise: at 10.6m average, it's not exceptional in absolute terms, but its 3.4m range makes it the Sea of Japan's most predictable site — ideal if you value planning certainty over peak clarity.
Choosing a "No-Bad-Days" Destination
- Best absolute + stable: Ishigaki, Kerama, Yonaguni
- Closest to Tokyo: Akinohama (Izu Oshima) — 2-hour jet foil from Takeshiba pier
- Mainland Pacific coast: Futone, Kushimoto, Osezaki Outer Ocean
- Sea of Japan: Omijima (Yamaguchi) — 3.4m range, stable winter visibility
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