Hachijojima Diving Visibility Guide — 17.1m Average from 336 Real Observations
2026-03-15
Located about 290km south of Tokyo, Hachijojima is the southernmost of the Izu Islands. Directly influenced by the Kuroshio Current, we analyzed its visibility using 336 real dive log observations. The annual average of 17.1m far exceeds Izu Oshima's Akinohama (14.3m) and Miyakejima (10.2m), making it the clearest water in the Izu Islands chain. September peaks at 21.9m, approaching Okinawa-level clarity.
17.1m
Annual avg
21.9m
Sep avg (peak)
13.6m
Jul avg (lowest)
336 obs
Real observations
Data period: January 2025 – March 2026
Monthly Visibility & Water Temperature
| Month | Vis (m) | Temp (°C) | Obs |
|---|---|---|---|
| Jan | 17.4m | 18.7°C | 48 |
| Feb | 16.9m | 18°C | 62 |
| Mar | 15.2m | 18.9°C | 44 |
| Apr | 15m | 19.8°C | 21 |
| May | 19.8m | 21.1°C | 28 |
| Jun | No data | - | 0 |
| Jul | 13.6m | 18.6°C | 18 |
| Aug | 17.3m | 22.8°C | 29 |
| Sep | 21.9m | 25.8°C | 29 |
| Oct | 16.4m | 26.2°C | 7 |
| Nov | 16.9m | 23.7°C | 22 |
| Dec | 16.8m | 22°C | 28 |
Hachijojima's Visibility Pattern: September Best, Surprising July Dip
September: 21.9m (annual peak)
Clear waters between typhoon events. Comfortable water temp at 25.8°C. The Kuroshio warm current flows steadily, and summer-stratified water reaches peak clarity. Exceeds Kerama, Okinawa (19.8m in September).
May: 19.8m (spring peak)
While mainland Izu struggles with spring plankton bloom, Hachijojima maintains nearly 20m visibility. The direct Kuroshio influence keeps coastal plankton growth less pronounced. Water temp 21°C suits a 5mm wetsuit.
July: 13.6m (surprising dip)
Data shows July as the year's lowest visibility month. This likely reflects Kuroshio path fluctuations and post-rainy-season water mixing. Water temp is also low at 18.6°C, suggesting cold water influence. However, with only 18 observations, this may shift with more data.
Winter (Dec–Feb): 16.8–17.4m (stable and clear)
Maintains 16–17m even in winter. While Izu Peninsula peaks in winter, Hachijojima is characterized by stable high visibility year-round. Water temp 18–22°C requires a 5mm wetsuit or drysuit.
Island Visibility Comparison: Where Hachijojima Stands
| Site | Avg Vis | Obs |
|---|---|---|
| Yakushima | 24.7m | 159 |
| Yonaguni | 24.5m | 4,826 |
| Ishigaki | 20.5m | 1,473 |
| Kerama | 19.3m | 1,554 |
| Hachijojima | 17.1m | 336 |
| Akinohama (Oshima) | 14.3m | 1,309 |
| Miyakejima | 10.2m | 941 |
Hachijojima: Tokyo's Clearest Island Getaway
In the Izu Islands, it leads Oshima (14.3m) and Miyakejima (10.2m) significantly, ranking just below Okinawa's Kerama (19.3m). About 10 hours by ferry from Tokyo Takeshiba, or 55 minutes by air — a rare chance to enjoy Okinawa-class visibility without flying south.
How the Kuroshio Creates Hachijojima's Clear Waters
Hachijojima's high visibility is a direct result of the Kuroshio Current. This warm current carries nutrient-poor oceanic water, which suppresses phytoplankton growth, resulting in clearer water.
However, the Kuroshio's path fluctuates. The ongoing Kuroshio Large Meander since 2017 often pushes the main flow south of Hachijojima, and cold-water eddies can affect both temperature and visibility. The July dip (13.6m visibility, 18.6°C water) may reflect this influence.
Reference: Japan Meteorological Agency 'Kuroshio Current Path' (https://www.data.jma.go.jp/gmd/kaiyou/data/shindan/b_2/kuroshio_stream/kuroshio_stream.html)
Hachijojima Diving: Wetsuit & Equipment Guide
| Season | Water Temp | Visibility | Suit |
|---|---|---|---|
| Jan–Apr | 18–20°C | 15–17m | 5mm – drysuit |
| May | 21°C | ~20m | 5mm wetsuit |
| Jul–Aug | 19–23°C | 14–17m | 5mm wetsuit |
| Sep–Oct | 25–26°C | 16–22m | 3–5mm wetsuit |
| Nov–Dec | 22–24°C | ~17m | 5mm wetsuit |
Access
By Air
About 55 min direct flight from Haneda Airport (ANA). 3 flights daily. Day-trip diving possible.
By Ferry
About 10hr 20min overnight ferry from Tokyo Takeshiba Pier (Tokai Kisen). Departs evening, arrives morning. Convenient for carrying heavy dive gear.
About the Data
336 observations collected from Hachijojima dive shop daily logs (Jan 2025 – Mar 2026). As a relatively new data source, June data is not yet available. Comparison with other island sites uses their full historical average. Visibility uses the mean of daily min/max values.
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