Echizen vs Tajiri vs Omijima: Sea of Japan's Big Three Compared
2026-03-16
Japan's Sea of Japan diving means three names: Echizen (Fukui), Tajiri (Tottori), and Omijima (Yamaguchi). Surprisingly, their annual averages are nearly identical (9.1–9.7m). But month by month, they're completely different. Tajiri's stunning August peak of 15.5m, Omijima's consistency, Echizen's winter closure — we compare all three using 6,000+ observations.
Annual Average: A Three-Way Tie
| Site | Annual Avg | Observations |
|---|---|---|
| Echizen | 9.7m | 2,653 |
| Tajiri | 9.4m | 1,392 |
| Omijima | 9.1m | 2,095 |
The gap between all three is just 0.6m. Annual averages say "they're all the same" — but seasonal patterns tell a very different story.
Monthly Comparison: Tajiri's August Dominates
| Month | Echizen | Tajiri | Omijima |
|---|---|---|---|
| Jan | Closed | 7.2m | 8.5m |
| Feb | Closed | 7.8m | 9.2m |
| Mar | Closed | 8.5m | 9m |
| Apr | 7.8m | 8.9m | 8.8m |
| May | 8.5m | 9.2m | 8.6m |
| Jun | 9.2m | 9.8m | 8.9m |
| Jul | 10.1m | 11.2m | 9.5m |
| Aug | 10.9m | 15.5m | 10m |
| Sep | 10.5m | 12m | 9.8m |
| Oct | 10.2m | 9.5m | 9.4m |
| Nov | 9m | 8m | 9m |
| Dec | Closed | 7m | 8.7m |
Tajiri's August 15.5m Is the Sea of Japan's Miracle
A site averaging 9.4m annually jumps to 15.5m in August — a 6m swing, far exceeding the other two. This is likely related to summer strengthening of the Tsushima Warm Current and coastal upwelling of clear cold water.
Each Site's Character
Echizen (Fukui)
- • Annual avg 9.7m (highest of three)
- • August peak 10.9m (moderate peak)
- • Closed winter (Dec–Mar) — Sea of Japan storms
- • 2,653 observations (most): highly reliable data
Tajiri (Tottori)
- • Annual avg 9.4m (middle)
- • August 15.5m stands out — summer transforms it
- • Largest seasonal swing (7.0–15.5m)
- • Open in winter but visibility drops
Omijima (Yamaguchi)
- • Annual avg 9.1m (lowest but marginal)
- • Smallest seasonal swing (8.5–10.0m)
- • Open year-round — reliable even in winter
- • "Same anytime" is Omijima's strength
Conclusion: When & Where to Go
Summer (Jul-Sep)
→ Tajiri, hands down. August's 15.5m is the Sea of Japan's best.
Spring/Fall (Apr-Jun, Oct-Nov)
→ Echizen is steady. Maintains ~9m throughout its operating season.
Winter (Dec-Mar)
→ Omijima is the only real option (Echizen closed, Tajiri low visibility).
About the Data
Echizen 2,653, Tajiri 1,392, Omijima 2,095 observations (total 6,140, 2006 – Mar 2026). Visibility is mean of daily min/max. Echizen's missing winter data reflects its closed season.
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