How the Kuroshio Large Meander Changed Diving Visibility in Japan (2017–2022)

What Is the Kuroshio Large Meander?

The Kuroshio Current is one of the world's most powerful ocean currents, flowing northward along Japan's Pacific coast. It carries warm, nutrient-poor (oligotrophic) water from the subtropics — and because low nutrients mean less phytoplankton, the water stays remarkably clear. In short: closer Kuroshio = better visibility.

Normally the Kuroshio flows close to the Kii and Izu Peninsulas, but every few decades it undergoes a dramatic southward deviation called a "large meander" (大蛇行, daisajaku). The large meander that began in September 2017 lasted until early 2022 — one of the longest on record (Japan Meteorological Agency). During this time, a persistent cold eddy formed near the Kii–Izu coastline, upwelling nutrients and reducing visibility.

Visibility Data: Before, During, and After the Meander

We split 46,000+ dive observations into three periods: pre-meander (2015–2016), during meander (2017–2021), and post-meander (2022–2025).

Average Visibility by Period (m)

Kushimoto shows the clearest meander signal: dropping from 12.9m (pre) to an average 11.6m during the meander (−1.3m), with a single-year low of 10.8m in 2018 — the worst recorded year. Kushimoto sits near Cape Shiono-misaki at the southernmost tip of the Kii Peninsula, directly in the Kuroshio's path. When the Kuroshio shifted south by 100–200 km, a cold counter-eddy formed along the Kii coast.

Yonaguni also declined (25.8m → 24.0m) but this reflects a separate long-term trend unrelated to the meander (see our "Long-term Visibility Trends" article). Echizen on the Sea of Japan showed virtually no change, confirming the meander's influence is limited to Pacific-coast Japan.

Year-by-Year Visibility (2015–2025)

Why Kushimoto Was Hit Hardest

Mikomoto (southern Izu Peninsula) showed a more complex pattern: visibility was actually above average in 2017–2019 (13.5–14.3m), before dropping to 12.5–12.6m in 2020–2021. The delayed response suggests that local Sagami Bay circulation modulated the meander's effect. Post-2022, Mikomoto continued declining — now driven by factors separate from the meander.

Recovery After the Meander (2022–Present)

The Japan Meteorological Agency declared the large meander's end in early 2022. Kushimoto rebounded to 12.5m in 2022, returning to near pre-meander levels. Futo also improved to 12.3–12.5m in 2023–2024. Mikomoto, however, continued declining (9.8m in 2025) — a reminder that oceanic visibility is shaped by multiple overlapping factors.

Practical Advice for Divers

• During a large meander: expect 1–2m visibility drop at Kii and Izu Peninsula Pacific-coast sites
• Unaffected areas: Okinawa Islands (Yonaguni, Kerama, Ishigaki), Sea of Japan sites (Echizen, Tajiri)
• After meander ends: Kii Peninsula sites like Kushimoto recover relatively quickly; Izu shows more site-specific variation

You can monitor the Kuroshio path through the Japan Coast Guard's Hydrographic and Oceanographic Department, which publishes real-time current charts. When a large meander is announced, consider shifting your Pacific-coast itinerary to more meander-insensitive sites.

Summary

• The 2017–2022 Kuroshio large meander reduced average visibility by ~1.3m at Kushimoto (Kii Peninsula)
• Worst single year: Kushimoto 2018 at 10.8m (−2.1m vs pre-meander)
• Izu Peninsula sites (Mikomoto, Futo) showed delayed and variable responses
• Okinawa and Sea of Japan sites showed no meander-related signal
• Post-2022 recovery confirmed at Kushimoto and Futo; Mikomoto declined due to separate factors