Does Kumomi Get Clearer with Stronger Currents? West Izu Current Analysis
2026-03-16
Kumomi in West Izu is popular among divers who love dramatic underwater topography, but it's also known for highly variable visibility. Data analysis reveals that current speed significantly affects visibility: fast current days (>0.3m/s) average 11.3m versus 7.5m on slow days (<0.1m/s) — a 3.8m difference. Kashiwajima shows an even more dramatic +4.6m gap.
11.3m
Kumomi (fast)
7.5m
Kumomi (slow)
13.4m
Kashiwajima (fast)
8.8m
Kashiwajima (slow)
Visibility by Current Speed
| Site | Fast (>0.3m/s) | Slow (<0.1m/s) | Diff |
|---|---|---|---|
| Kumomi | 11.3m | 7.5m | +3.8m |
| Kashiwajima | 13.4m | 8.8m | +4.6m |
Why Stronger Currents Mean Better Visibility
1. Clean Offshore Water Flows In
Strong currents indicate active supply of offshore water. Oceanic water has less plankton and suspended matter than coastal water, resulting in better visibility. When Kuroshio-influenced warm water flows in, clarity can improve dramatically.
2. Turbid Coastal Water Gets Flushed
Without currents, turbid water from rain and rivers stagnates near shore. Strong currents flush this murky water out and replace it with clean oceanic water.
3. West-Facing Sites Benefit Most
West-facing sites like Kumomi and Kashiwajima directly face the open ocean, making them prime beneficiaries of offshore current flow. East-facing or bay-enclosed sites see less of this effect.
Practical Advice: Using Current Forecasts
- Check current forecasts (Japan Coast Guard ocean current charts, SCF, etc.) in advance. When the Kuroshio approaches, expect better visibility at Kumomi and Kashiwajima.
- However, strong current days mean more challenging drift diving. Better visibility comes with higher skill requirements.
- When planning a Kumomi dive on a weak current day, expect around 7–8m visibility as a baseline.
About the Data
Current speed data from Open-Meteo Marine API (ocean current velocity). Kumomi analysis is based on 1,980 observations, Kashiwajima on 925. Current speed thresholds (0.1m/s, 0.3m/s) were set based on data distribution.
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