Okinoshima Island

islandsnorkelingcoral reefmarine lifebeach

Chiba · Tateyama

34.9789°N, 139.8311°E

Okinoshima is a small island connected to the Tateyama coast by a 500-meter sandbar, creating a tide-dependent land bridge that disappears at high tide. The island's surrounding waters are part of the northernmost coral reef ecosystem in Japan, sustained by the warm Kuroshio Current. Snorkeling here reveals a surprising diversity: tropical fish (damselfish, wrasses, butterflyfish), sea anemones, and over 40 species of coral — just from central Tokyo.

The island itself is a short walking loop through coastal forest, with small beaches, tide pools, and a cave shrine dedicated to maritime safety. The ecosystem's proximity to Tokyo makes it a rare example of accessible marine biodiversity without requiring flights to Okinawa.

Essential Information

Opening Hours

Accessible at low tide (check tide tables) | No set hours — tide-dependent

Closed: No formal closures | Not accessible at high tide

Entrance Fee

Free | Snorkeling gear rental: ¥1,500/day (nearby beach shops)

Best Season

May-October (snorkeling season) | July-September for tropical fish | April-June for clearest water

Visit Duration

2-3 hours (island walk + snorkeling)

Getting There

Access Information

Okinoshima, Tateyama City. Near Tateyama Station. Accessible at low tide; check tide tables. Free entry. Snorkeling gear rental available at nearby beach shops (¥1,500/day). Best visited May–October.

Insider Guide

Premium

**Tide timing:** The sandbar is walkable 2-3 hours before and after low tide. High tide completely submerges the connection — plan around tidal charts available at Tateyama tourist info. Summer low tides (July–August) occur in early morning and late afternoon, ideal for avoiding midday heat. **Snorkeling zones:** The north side (facing the bay) has calm, shallow water ideal for beginners and families. The south side (open ocean) has stronger currents but better coral formations and larger fish. Intermediate snorkelers should explore the south rocky areas 30 minutes before low tide when visibility peaks. **Marine life calendar:** Summer (July–September) brings tropical species carried by the Kuroshio Current — clownfish, parrotfish, and occasional sea turtles. Spring (April–June) is clearest water due to plankton bloom decline. Autumn sees juvenile fish sheltering in the reef. **Conservation note:** The reef is monitored by Tateyama Marine Science Museum. Visitors are asked to avoid standing on coral (wear reef-safe shoes), use reef-safe sunscreen, and not remove shells or creatures. The fragile ecosystem faces pressure from warming water temperatures.

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