Why Is Kannoura's Visibility So Low? 4m Gap from Same-Prefecture Kashiwajima
2026-03-16
Despite both being in Kochi Prefecture, Kannoura averages 9.1m visibility while Kashiwajima averages 13.1m — a 4m gap. The probability of reaching 15m+ visibility is 44.4% at Kashiwajima versus just 4.4% at Kannoura. What causes such a dramatic difference? We examine the data and geographic factors.
9.1m
Kannoura avg
13.1m
Kashiwajima avg
4.4%
Kannoura 15m+ prob
44.4%
Kashiwajima 15m+ prob
Kannoura vs Kashiwajima: Same Prefecture, Different Worlds
| Site | Avg Vis | 15m+ Prob | Best Month | Best Avg |
|---|---|---|---|---|
| Kashiwajima | 13.1m | 44.4% | Aug | 16.2m |
| Kannoura | 9.1m | 4.4% | Nov | 11.5m |
Three Reasons for Kannoura's Low Visibility
1. Northeast of Cape Muroto = Kuroshio Shadow
Kannoura sits northeast of Cape Muroto. The Kuroshio flows northeast along the Pacific coast, but after rounding Cape Muroto, the area around Kannoura falls into a 'shadow zone' that doesn't directly benefit from the current. Kashiwajima, at Shikoku's southwest tip, directly faces the Kuroshio and receives clean oceanic water.
2. River Runoff (Nonegawa River)
The Nonegawa River flows into the Kannoura area, bringing fresh water and sediment after rain. During the rainy season and after typhoons, river runoff significantly reduces visibility. Kashiwajima has no major rivers nearby, minimizing this effect.
3. Shallow Continental Shelf
Kannoura has a relatively shallow and wide continental shelf where bottom sediment is easily stirred up by waves and tidal currents. Even moderate waves can suspend mud and sand from the shallow seafloor. Kashiwajima has deep water close to shore, reducing sediment resuspension.
Kannoura Monthly Visibility: November Is Best
| Month | Avg Vis |
|---|---|
| Jan | 9.3m |
| Feb | 8.5m |
| Mar | 7.8m |
| Apr | 7.5m |
| May | 8.2m |
| Jun | 8m |
| Jul | 9m |
| Aug | 10.1m |
| Sep | 10.5m |
| Oct | 10.8m |
| Nov | 11.5m |
| Dec | 9.8m |
Tips for Diving at Kannoura
- Best timing is autumn (October–November). After typhoon season recovery, 10m+ visibility is achievable.
- Avoid diving 2–3 days after rain due to lingering river turbidity. Wait for 3+ consecutive sunny days.
- For visibility-focused dives, Kashiwajima in the same prefecture is far superior. Choose Kannoura for its macro life and abundant fish — attractions beyond visibility.
About the Data
Kannoura data collected from dive shop daily logs. Comparison with Kashiwajima uses full historical averages. Monthly data represents all-year averages. The 15m+ probability is the percentage of observation days recording 15m or higher.
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