One sea, five regions,
four seasons
One sea, five regions, four seasons.
Korea’s seas split sharply in season, water temperature and visibility by region because of latitude and current structure. Average water temperature runs South Sea > East Sea > West Sea; peak season is broadly late spring to autumn (May–Oct), and the wild cards are typhoon season (Jul–Sep) and West Sea tides. This page gathers the best season, monthly water temperature, visibility, current and suit for all five regions on one screen.
Three currents that divide Korea’s seas
① Average water temperature: South Sea > East Sea > West Sea. ② Peak season is May–Oct (per PADI Korea, spring and autumn are best). ③ Typhoons and tides are the biggest variables — influencing typhoons peak in August (1.2 on average).
When and which region to go
Gangneung Marine Park wreck and Wangdolcho offshore reef. Exception — Yangyang Ingu Anemone Garden is best in winter (the frilled-anemone blooming season).
June field observations show low visibility of 5–8m; autumn is relatively clear. Beomseom, Munseom, Seopseom.
Warm water allows diving into mid-October. Yokjido. Offshore islands (Tongyeong Hongdo, Geomundo) depend on weather and tides.
From Aug–Oct the Kuroshio warm current brings tropical fish north. Winter access is limited by rough seas and swell (Dokdo landing is impossible above 3–5m swell).
The best ‘tide (slack)’ matters more than the best ‘season’. Media often feature summer (after mid-July).
Ulleung·Dokdo Jun–Oct(Korea’s clearest water) · Jeju Sep–Nov(soft coral + autumn visibility). Note: for both regions, boat departures are sensitive to weather.
Surface temperature by region × period
Midsummer high ~27°C(Yokjido surface) ↔ midwinter low −1.7°C(Incheon Feb). The bottom runs colder.
※ Dashed cells are approximate estimates (verify needed), set only within ranges consistent with the 2024 official annual means. Region-level monthly primary sources are not yet secured. Sources · PADI (aggregated), National Institute of Fisheries Science (West Sea winter −1.7), internal data (Munseom·Ulleung [confirmed]).
Some sites such as Ssangjeongcho hold 30–40m year-round — Korea’s clearest water, shaped by open-sea and volcanic-rock terrain.
SsangjeongchoThe West Sea is about ‘tides (slack)’ more than ‘season’
The West Sea has a large tidal range, so currents are strong and flood and ebb alternate roughly every 6 hours. The range peaks at spring tides (sari, 大潮) and bottoms at neap tides (jogeum, 小潮) with the moon phase. In spring-tide narrows the current can exceed 5 knots — beginners should avoid it. Slack water (jeongjo, 停潮) = the short transition when the current nearly stops, the only safe window to enter.
Days with a small tidal range. Time entry and exit using KHOA (Korea Hydrographic and Oceanographic Agency) tide and current forecasts.
Maximum tidal range. Currents over 5 knots in narrows — beginners avoid. Gyeokryeolbiyeoldo and Sibidongpado only in the short window around slack.
The East Sea and Ulleung/Dokdo have a small tidal range, so swell, wind waves and current — not tides — are the entry variables (Dokdo landing is impossible above 3–5m swell). Jeju and South Sea offshore islands are sensitive to both tides and weather. And even at slack, the West Sea is usually low-visibility.
Recommended suit by temperature band
East Sea bottom 2~4°C(drysuit) ↔ midsummer surface 24~27°C(wetsuit). Adjust for personal cold tolerance, dive time and depth.
Midsummer surface layer — South Sea, Jeju, Ulleung.
Late spring and autumn, most regions.
Early spring and late autumn, East Sea.
East Sea winter and deep dives (bottom 2–4°C).
Even with an 18–21°C summer surface, the bottom drops to 2–4°C. Yangyang Ingu Anemone Garden (best in winter, bottom ~35m) is the signature drysuit environment.
Effectively off-season — Incheon Feb −1.7°C plus low visibility.
A wetsuit is enough. For deep or long dives, 5mm + hood.
A year of recommended regions by period
Anemone-bloom diving (drysuit, low visibility, deep). West Sea not recommended (icing, low visibility); Ulleung/Dokdo access limited.
Water-temperature recovery. PADI rates May as best (though visibility trails autumn).
Ulleung·Dokdo season opens (abundant fish, 20–30m visibility); East Sea beach season. After mid-July, West Sea tide exposure rises. Typhoons begin.
Highest water temperature (surface ~24–27°C) but the most typhoons (1.2 on average) — risk of offshore boat departures being cancelled.
Jeju at its best (soft coral + autumn visibility), South Sea into mid-October, tropical fish moving north at Ulleung·Dokdo. Best for visitors (September, with residual autumn typhoons at 0.8).
Water temperature drops sharply. East Sea deep dives need a drysuit; Jeju keeps visibility but temperature falls.
For the West Sea, check tides (slack) before season — the KHOA tide table is essential.
For offshore boats (Wangdolcho, Ulleung/Dokdo, Tongyeong offshore islands), weather and swell are the top variable.
- Region-level quantitative values — most lack primary sources, so they are null+pending in the data. Dashed cells in the table are approximate estimates, set only within ranges consistent with the 2024 official annual means.
- Ulleung·Dokdo visibility 20–30/40–50m — aggregated from multi-source reputation. Region-level monthly primary sources not secured.
- Spring-tide current 5 knots+ · tide structure — cited from fishing guides, not primary-verified. Always confirm entry/exit with KHOA tide tables / current forecasts.
- Suit spec recommendations — no official spec-recommendation source secured. This table is a general guide based on data and aggregation.
The best time,
the best sea
Pick your season, plan your dive.