Izu vs Okinawa: Diving Visibility & Water Temp Compared with 19,000 Real Observations

March 11, 2026 · 19,855 real observations

The Truth About Japan's Two Premier Dive Regions

Izu Peninsula and Okinawa — Japan's two most visited dive regions. But their characteristics differ significantly. We compare 19,855 real observations monthly across 6 Izu Peninsula sites (IOP, Futo, Mikomoto, Kumomi, Osezaki, Koganezaki) and 3 Okinawa areas (Yonaguni, Ishigaki, Kerama). Does data confirm that 'Okinawa is always clearer,' and are there moments when Izu approaches Okinawa's level?

Overall Comparison

Metric	Izu Peninsula	Okinawa	Note
Annual avg visibility	12.0m	21.4m	Okinawa leads by ~9m
Winter visibility (Dec–Feb)	15.6m	21.7m	Gap narrows to 6m in winter
Spring visibility (Mar–May)	10.7m	22.4m	Izu hit by spring plankton bloom; 11.7m gap
Summer visibility (Jun–Aug)	11.0m	23.3m	Widest gap in summer–autumn due to typhoons/rain
Annual avg water temp	21.5°C	25.3°C	Okinawa supports wetsuit diving year-round
Winter water temp (Jan)	16.5°C	23.5°C	Izu January requires 5mm+ wetsuit
Total observations	12,010件	7,845件	Izu has more accumulated data

Monthly Visibility & Gap (All 12 Months)

Month	Izu	Okinawa	Gap (Okinawa leads)	Izu temp	OK temp
Jan	16.2m	21.5m	+5.3m	16.5°C	23.5°C
Feb	15.5m	21.6m	+6.1m	15.8°C	23.3°C
Mar	12.4m	22.4m	+10m	15.9°C	23.6°C
Apr	10m	22.4m	+12.4m	16.8°C	23.8°C
May	9.7m	22.5m	+12.8m	18.2°C	25.8°C
Jun	10.9m	22.4m	+11.5m	20.9°C	27°C
Jul	10.5m	23.6m	+13.1m	22.9°C	28°C
Aug	11.6m	23.9m	+12.3m	24.5°C	27.8°C
Sep	11.8m	24.3m	+12.5m	25.1°C	28.4°C
Oct	12.6m	22.8m	+10.2m	24°C	27.3°C
Nov	12.9m	22.1m	+9.2m	21.5°C	26.1°C
Dec	15.2m	22.1m	+6.9m	18.7°C	24.8°C

Red/bold gap = Okinawa advantage is large. Spring–autumn (Apr–Sep) shows 12m+ differences.

3 Key Truths the Data Reveals

① The gap is smallest in winter (January–February)

January's gap is just 5.3m (Izu 16.2m vs Okinawa 21.5m) — the smallest of the year. Izu's winter clarity peaks because Kuroshio influence weakens and plankton density drops. January (16.2m), February (15.5m), and December (15.2m) are Izu's best months. Okinawa maintains 21–24m year-round, so the gap narrows but never reverses.

② The gap widens most in summer–autumn (July–September)

July (13.1m gap) and September (12.5m gap) show the widest differences. In Izu, visibility doesn't fully recover from heavy summer rains, and typhoons add waves and turbidity. Meanwhile, Okinawa (Yonaguni, Ishigaki, Kerama combined) reaches peak clarity in summer, hitting 24.3m in September — the annual maximum. This data supports Okinawa's reputation as a summer dive paradise.

③ Spring plankton bloom (April–May) is Izu's worst enemy

April (10.0m) and May (9.7m) are Izu's worst months. As spring water temperatures rise, plankton blooms explosively, crashing visibility. The gap with Okinawa reaches 12.4–12.8m during this period. Divers planning Izu trips around Golden Week should factor in this spring plankton bloom risk.

Izu's Best and Worst Months

Rank	Month	Visibility	Water temp	Note
1	Jan	16.2m	16.5°C	Clarity peak
2	Dec	15.2m	18.7°C	Winter clarity
3	Feb	15.5m	15.8°C	Winter clarity
4	Nov	12.9m	21.5°C	Autumn recovery
5	May	9.7m	18.2°C	Spring bloom = worst

Which Should You Choose?

Choose Izu If...

✓ You're diving in winter (Dec–Feb)
✓ You prioritize access from Tokyo/Kanagawa
✓ You prioritize nudibranchs and fish density
✓ You want more dives per budget
✗ Avoid April–June (spring bloom & rainy season)

Choose Okinawa If...

✓ Visibility is your top priority
✓ You want stable conditions year-round
✓ You're diving in summer–autumn (Jul–Sep)
✓ You prefer warm water diving
△ Typhoon season (Aug–Sep) = flight cancellation risk

Summary

The data is clear: Okinawa (21.4m annual avg) leads Izu (12.0m) by about 9m year-round. But the notion that 'Izu winters are poor' is wrong — December through February delivers 15–16m of excellent visibility. The data-driven optimal strategy: visit Izu in winter when the gap narrows, and fly to Okinawa in summer when you want maximum clarity.

Data source: scraped from public dive logs. Izu Peninsula (IOP/Futo/Mikomoto/Kumomi/Osezaki/Koganezaki): 12,010 obs; Okinawa (Yonaguni/Ishigaki/Kerama): 7,845 obs.