What Counts as "Good" Visibility? It Depends on Where You Dive
2026-03-16
When a local diver says 'the water is great today,' what they mean varies enormously by location. At Yonaguni, 'great' means 30m+. At Hirasawa, it means about 12m. Without understanding these local standards, visitors may feel disappointed at a new site. Let's use data to define what 'good' really means at each location.
Yonaguni's "good"
28m+
Top 25%
IOP's "good"
17m+
Top 25%
Hirasawa's "good"
11m+
Top 25%
Defining "Locally Good": The Top 25% Threshold
We define 'locally good visibility' as the top 25th percentile (third quartile) of all observations at each site. This represents a level achieved roughly 1 in 4 times — the threshold where locals would say 'today's a good day.'
By-Site Visibility Distribution
| Site | Bottom 25% | Median | Top 25% "Good" | Avg | Obs |
|---|---|---|---|---|---|
| Yonaguni | 20m | 25m | 28m | 24.5m | 4,826 |
| Kerama | 15m | 20m | 23m | 19.3m | 1,554 |
| IOP | 10m | 13m | 17m | 13.8m | 3,151 |
| Akinohama | 10m | 15m | 18m | 14.3m | 1,309 |
| Futo | 8m | 11m | 15m | 11.5m | 3,493 |
| Kushimoto | 8m | 12m | 15m | 11.9m | 3,168 |
| Hirasawa | 6m | 8m | 11m | 8.8m | 2,696 |
| Echizen | 7m | 9m | 12m | 9.7m | 2,652 |
Managing Expectations Increases Satisfaction
20m at Yonaguni is "below average"
Yonaguni's median is 25m. At 20m, you're near the bottom 25% — locals would say 'not great today.' But for mainland divers, 20m is dreamlike. Judge by local standards, not your home site, for accurate expectations.
12m at Hirasawa is "jackpot"
Hirasawa's top 25% is 11m. If you get 12m, that's a legitimate 'great day.' Rich in macro life and enjoyable even with lower visibility, but at 12m you can appreciate the terrain too — perfect conditions.
18m at IOP means "crystal clear today!"
IOP's top 25% is 17m. At 18m, even regulars get excited. Most common when the Kuroshio approaches in winter — when you hit these conditions, the underwater world looks like a dive magazine photo.
Practical Advice
- Before visiting a new site, check its average visibility
- Don't just accept 'it's good today' — ask for specific numbers
- Use our forecasts to understand each site's 'normal range'
- Use the median as your baseline — anything above that is a bonus
About the Data
Data is based on real observations from dive shop daily logs. Quartiles are calculated from all observations. Observation periods and counts vary by site.
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