Osezaki Complete Visibility Guide — Bay, Open Sea, Point & Futone (4,300 Obs)
2026-03-16
Osezaki sits at the western tip of the Izu Peninsula, one of Japan's premier dive areas. With 4 zones — Bay, Open Sea, Point, and offshore Futone — visibility can differ by 5m+ depending on which point you choose. We analyzed 4,300+ real observations to fully dissect each zone.
4-Zone Annual Averages
Advanced drift site offshore. Highest visibility thanks to open ocean water
Beautiful soft corals. Winter peaks at 12.8m. Summer drops to 8.7m in July
Between open sea and bay. Winter matches open sea, summer drops toward bay levels
Beginner training & macro photo mecca. Aug 5.9m is annual low. Even Jan 11.8m is below other zones
Monthly Visibility Heatmap
| Zone | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Futone | 14.8 | 14 | 11.9 | 11.4 | 10.4 | 12.1 | 10.9 | 11.2 | 13.2 | 13.2 | 12.3 | 12.9 |
| Open Sea | 12.8 | 12.6 | 11.1 | 9 | 10.4 | 11.5 | 8.7 | 10.3 | 10.9 | 9.7 | 10 | 12.8 |
| Point | 13.2 | 13.6 | 10.5 | 9.2 | 12.3 | 11 | 8.7 | 8.9 | 8.8 | 10.6 | 9.9 | 13.3 |
| Bay | 11.8 | 10.7 | 8.6 | 6.6 | 7.8 | 7.5 | 6.5 | 5.9 | 6.5 | 6.5 | 7.8 | 9.5 |
The Science Behind Zone Differences
Why the Bay Is Low: Enclosed Geography & Sandy Floor
The bay is enclosed on three sides, limiting clean ocean water exchange. Its sandy bottom stirs up easily with fin kicks, dropping to 5.9m in summer when diver traffic peaks. Yet this environment creates a haven for sand-dwelling creatures — perfect for macro photography.
Why Open Sea & Point Are Better: Current Flow
The open sea area receives direct inflow from Suruga Bay's offshore water, reaching 12.8m in winter — close to Futone. The Point sits at the boundary, combining open sea characteristics (good days: 13m+) with bay influence (poor days: 9m range) depending on current direction.
Why Futone Tops: Full Open Ocean
Futone is an offshore pinnacle fully exposed to open ocean currents. Its 12.3m annual average is the area's highest. January peaks at 14.8m with relatively small seasonal variation (4.4m range). Requires drift diving skills — advanced divers only.
Best Zone by Purpose
Best Visibility
Futone (12.3m) → Winter Jan 14.8m
Macro Photography
Bay (7.6m) → Bio diversity over clarity
Beginner Training
Bay → Calm, beach entry
Wide-Angle & Topography
Open Sea (10.6m) → Soft coral gardens
About the Data
4 Osezaki zones (Bay 2,016 / Open Sea 931 / Point 434 / Futone 936) totaling 4,317 observations (2006–Mar 2026). Visibility = mean of daily min/max.
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