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April Diving: Where to Go During Japan's Worst Visibility Month

2026-03-16

April averages 12.3m nationally — the year's worst month. The spring bloom peaks along Pacific Honshu: IOP 10.1m, Futo 9.5m, Kushimoto 10.0m all hit annual lows. But "April is undiveable" is wrong. Yonaguni 25.0m, Ishigaki 21.3m, and surprise performer Shirahama 16.1m offer clear alternatives. Here's your April escape plan.

Sites at Their Annual Worst in April

SiteApr AvgNote
Futo9.5mAnnual low
Kushimoto10mAnnual low
IOP10.1mAnnual low

Futo's 9.5m is nearly 6m below January's 15.4m. A 40% drop in 3 months — that's the power of the spring bloom.

April Escapes: Bloom-Free Sites

SiteApr Avg Vis
Yonaguni25m
Ishigaki21.3m
Kerama18.8m
Shirahama16.1m
Akinohama13.6m

Shirahama 16.1m: The Surprise Performer

Nanki-Shirahama benefits strongly from the Kuroshio, limiting spring bloom impact. It maintains 16.1m even in April — an accessible gem reachable as a day trip or overnight from Honshu.

Akinohama 13.6m: The All-Season Stable Site

Oshima's Akinohama has minimal year-round visibility variation, holding steady at 13.6m even in April — largely immune to the spring bloom.

Monthly Trend: April Is the Bottom

MonthNational Avg
Jan16.1m
Feb15.4m
Mar13.6m
Apr12.3m
May12.5m
Jun12.7m
Jul12.6m
Aug13.1m
Sep13.1m
Oct12.9m
Nov13.4m
Dec15.4m

April Has Its Upsides Too

Marine Life

  • • Peak nudibranch season (especially Izu)
  • • Lumpfish juveniles visible (Kanto northward)
  • • Plankton-rich = abundant food for macro life

Practical

  • • Water warming, wetsuit transition period
  • • Pre-Golden Week pricing
  • • Fewer divers, relaxed pace

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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