Spring Break Diving Visibility: Is Late March the Worst Timing?
2026-03-16
Planning a spring break dive trip? Late March in Izu means a sharp drop from winter's peak. IOP plummets from 17.7m to 13.7m — a 4m decline. The spring bloom (massive phytoplankton growth) kicks in, dragging down Pacific Honshu visibility across the board. But change your destination and the story flips — Yonaguni 24.9m, Ishigaki 22.7m are waiting.
Pacific Honshu: The February to March Plunge
| Site | Feb | Mar | Change |
|---|---|---|---|
| IOP | 17.7m | 13.7m | -4m |
| Futo | 14.8m | 11.6m | -3.2m |
| Kushimoto | 12.3m | 10.8m | -1.5m |
| Koganezaki | 15.2m | 15.8m | +0.6m |
Koganezaki Is the Exception
West Izu's Koganezaki actually improves slightly to 15.8m in March. Its bay geography and current patterns may buffer it from the spring bloom.
Okinawa & Islands: Clear Water Even in March
| Site | Mar Avg Vis |
|---|---|
| Yonaguni | 24.9m |
| Ishigaki | 22.7m |
| Kerama | 18.5m |
The southwestern islands are largely unaffected by the spring bloom. The Kuroshio brings nutrient-poor oceanic water that doesn't support explosive plankton growth.
What Is the Spring Bloom?
As spring brings longer days and warming water, phytoplankton rapidly multiply using nutrients accumulated over winter. This 'spring bloom' is the primary cause of the greenish murky water. In Japan, it's most pronounced from March to May, especially along the coast.
Reference: JMA Ocean Health Report, NASA Ocean Color
Conclusion: Where to Go for Spring Break
Avoid
- • East Izu (IOP, Futo): in free fall
- • Kushimoto: 10.8m, near annual low
Recommended
- • Yonaguni (24.9m): hammerhead season overlap
- • Ishigaki (22.7m): manta season begins
- • Koganezaki (15.8m): best Izu option
About the Data
Monthly aggregation of 46,000+ observations from 42 nationwide dive sites (2006 – Mar 2026). Visibility is mean of daily min/max.
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