Korea has three distinct seas — the West Sea, East Sea, and South Sea — each with different depths, ecosystems, and coastal experiences. The Korean government designates May 31st as National Oceans Day (바다의 날), a reflection of how central the sea is to life here.
For anyone visiting or living in Korea, the sea is never far. But these three bodies of water are more different than most people expect.
How Korea's Coastlines Compare
Korea's coastline stretches in three directions, and with that comes three distinct marine environments. The differences shape everything from the beaches you'll visit to the seafood on your table — including gim (Korean seaweed), now gaining recognition worldwide.
Here's what sets each sea apart.
West Sea: Tidal Flats and the Boryeong Mud Festival
The West Sea (서해) sits between the Korean Peninsula and China. Fed by sediment from major rivers — China's Yellow and Yangtze, Korea's Han and Geum — it's shallow, nutrient-rich, and filled with expansive tidal flats.
The gentle waters and proximity to Seoul make West Sea beaches popular with families. Incheon's Eurwangni Beach is one of the most accessible from the capital.
Beyond swimming, the West Sea's tidal flats are the main draw. The dramatic difference between high and low tides reveals mudflats teeming with shellfish and marine life — often called "nature's treasure houses." Visitors can join guided tidal flat experiences to dig for clams and observe the ecosystem up close.
The annual Boryeong Mud Festival, held each July and August at Daecheon Beach, draws visitors from around the world. The local mud is known for its mineral content, with reported benefits for skin detoxification and anti-aging.
East Sea: Deep Blue Beaches and Surfing Culture
The East Sea (동해) opens toward the Pacific. With an average depth of 1,361 meters and few islands, its coastline features some of Korea's most striking sandy beaches.
Yangyang has become Korea's surfing capital. Consistent waves and a growing surf culture draw both beginners and experienced surfers year-round.
Gangneung, reachable from Seoul by KTX train in under two hours, offers wide beaches like Gyeongpo — plus a local specialty worth seeking out: ojingeo sundae (오징어 순대), squid stuffed with a savory filling.
South Sea: Islands, Oysters, and History
The South Sea (남해) is defined by its complex coastline and dense archipelago, including Jeju Island. Shallower than the East Sea and warmed by year-round currents, it supports a thriving fishing and aquaculture industry. Oysters, in particular, are produced here in abundance.
This sea also carries deep historical significance. During the Imjin War (1592–1598), Admiral Yi Sun-sin used the South Sea's intricate geography and tidal currents to win decisive naval victories, including the Battle of Hansan Island.
And then there's Jeju Island — surrounded by emerald waters visible from every direction. Head east for sunrise, west for sunset. Hyeopjae Beach, on Jeju's western shore, is one of the most photographed coastlines in Korea.
Korea's seas are as diverse as the country itself. Whether you're walking a West Sea mudflat at low tide, catching waves off Yangyang, or watching the sun set over Jeju's emerald waters — the coastline is one of the most underrated parts of any trip to Korea.
| Edited by Sia Shin, The Pylon Square
