The Bohai Sea (Chinese: 渤海; pinyin: Bó Hǎi; Zhuyin Fuhao: ㄅㄛˊ ㄏㄞˇ; meaning "Bo Sea") is a gulf or inland sea with an area of about 77,000 km² (30,000 sq mi) on the east coast of Mainland China. It is the northernmost and innermost part of the Yellow Sea, connected to it through the Bohai Strait. The average depth of the Bohai Sea is about 18 meters (59 feet), and its deepest point is approximately 80 meters (260 feet), found in the northern part of the Bohai Strait.

The Bohai Sea is surrounded by three provinces and one direct-administered municipality: Liaoning Province (in Northeast China), Hebei Province, Tianjin Municipality (in North China), and Shandong Province (in East China). It is the center of the Bohai Economic Rim. Its location near Beijing, the capital of China, and Tianjin makes it one of the busiest sea routes in the world. The entrance to the Bohai Sea is part of China’s territorial sea because of the Miaodao Islands. In 1958, China declared the Bohai Sea to be part of its inland waters.

History

During the Pleistocene, the Bohai Sea experienced many changes in sea level caused by ice ages. Evidence from sediment samples taken from the seafloor shows that floodplain conditions existed during times when sea levels were low.

Throughout Chinese history, the Bohai Sea was important for both strategy and trade. During the Tang Dynasty, it connected China to the Bohai Kingdom, an early medieval state in present-day northeast China and parts of the Korean Peninsula. Trade and diplomatic exchanges between China, Korea, and Japan often passed through the Bohai Sea, linking it to a larger East Asian maritime network. During the Liao (907–1125) and Jin (1115–1234) dynasties, controlled by the Khitan and Jurchen peoples, controlling the Bohai region was key to their power in northern China. These dynasties built naval bases and fortified ports along the coast.

In the Yuan Dynasty (1271–1368), the Bohai Sea became more important as maritime trade expanded under a unified empire. Naval bases were built along the coast, and shipping routes were developed to support military and commercial activities. The Ming (1368–1644) and Qing (1644–1912) dynasties used the Bohai region for patrols and defense, especially during the Ming era when Japanese pirates (wokou) posed threats. Ports like Yingkou and Dagu were important for trading salt, grain, and fish.

Until the early 20th century, the Bohai Sea was often called the Gulf of Zhili or Gulf of Beizhili. Western romanization systems used names like "Jili" or "Pechihli" for these regions. Zhili and North Zhili were historic provinces near Beijing, now part of Hebei Province.

In the late 19th century, the Bohai Sea became a major site of military conflict. During the First Sino-Japanese War (1894–1895), key naval battles occurred near the Bohai Sea. The Battle of the Yalu River in 1894, fought near the Bohai Sea’s eastern edge, resulted in a major defeat for the Qing navy’s Beiyang Fleet. This loss allowed Japanese forces to move further into the Bohai region. In early 1895, Japanese troops invaded the Shandong Peninsula and captured Weihaiwei, a heavily fortified naval base at the Bohai Sea’s eastern entrance. The fall of Weihaiwei led to the Qing government’s defeat and the signing of the Treaty of Shimonoseki, which required China to cede Taiwan and recognize Korea’s independence.

Later, during the Boxer Rebellion (1899–1901), the Bohai Sea was again strategically important. As anti-foreign protests spread to Beijing, the port city of Tianjin, located on the Bohai Sea’s western edge, became a key location for foreign military action. In June 1900, an international alliance of eight nations launched an amphibious attack on the Dagu Forts, which protected the Hai River and access to Tianjin and Beijing. After capturing the forts, allied forces advanced inland, reaching Beijing and forcing the Qing court to flee. This led to the signing of the Boxer Protocol in 1901.

Geography

The Bohai Gulf contains three major bays: Laizhou Bay to the south, Bohai Bay to the west, and Liaodong Bay to the north. The provinces with coastlines along the Bohai Sea, listed clockwise from the south, are Shandong, Hebei, Tianjin (Tientsin), Hebei again, and Liaoning. Major rivers that flow into the gulf include the Yellow River, Xiaoqing River, Hai River, Luan River, Dai River, Daling River, Xiaoling River, Liao River, and Daliao River. Important oil reserves near the gulf include the Shengli Field. Notable islands or island groups in the gulf are the Changshan Archipelago, Juehua Island, Bijia Mountain, Changxing Island, Xizhong Island, the East/West Mayi Islands, Zhu Island, and She Island.

The opening of the Bohai Sea is located between the southern tip of the Liaodong Peninsula, near Lüshunkou District in Dalian, and the northernmost point of the Shandong Peninsula, at Cape Penglai, with the Changshan Archipelago marking the boundary. Because the Bohai Sea is near Beijing and the surrounding provinces have over 210 million people, the Bohai Strait, which connects the Bohai Gulf to the Yellow Sea, has become one of the busiest sea routes. The strait is divided into several channels by the Changshan Island Chain, which crosses its southern half. These channels include:

• Laotieshan Channel (Lau-ti-shan Channel), the widest and deepest
• Daqin Channel
• Xiaoqin Channel
• North Tuoji Channel
• South Tuoji Channel
• Changshan Channel, the most direct route to Tianjin
• Dengzhou Channel (Miaodao Channel or Miaodao Strait), the closest to the shore but the shallowest.

Major ports

There are five major ports along the Bohai Sea with cargo amounts over 100 million tons. The port of Tangshan is split into two parts: Jingtang and Caofeidian. These are the major ports:

• Port of Yingkou (营口港; 營口港)
• Qinhuangdao Port (秦皇岛; 秦皇島港)
• Port of Jingtang (京唐港)
• Port of Tangshan (唐山港)
• Port of Tangshan Caofeidian (曹妃甸港)
• Tianjin Port (天津港)
• Port of Huanghua (黄骅港; 黃驊港)

For reporting numbers, Caofeidian and Jingtang are often counted as one port. The ports of Dalian and Yantai are usually included in the Bohai Sea region, even though they are technically outside the sea’s boundaries. The Port of Longkou handled 70 million tons of cargo in 2013 and is expected to reach 100 million tons soon.

Major cities along the Bohai Sea coast

List of Chinese Cities:

Liaoning: Dalian, Yingkou, Panjin, Jinzhou, Huludao, Lüshun, Xingcheng
Hebei: Qinhuangdao, Beidaihe, Tangshan, Cangzhou
Tianjin: Binhai
Shandong: Yantai, Zhifu, Penglai, Longkou, Zhaoyuan, Laizhou, Muping, Fushan, Weifang, Hanting, Dongying, Kenli, Binzhou

Hydrocarbon resources

The Bohai Bay has important oil and gas supplies that contribute to much of China's offshore production. The main field in the area, called Shengli, has been used since the 1960s. It still produces about half a million barrels of oil each day, but its output is decreasing. Most production in the region is managed by major Chinese companies (China National Offshore Oil Corporation, or CNOOC, was mainly established for this area), though foreign companies like ConocoPhillips and Roc Oil Company also operate there. The Gudao Field, located in the Zhanhua sedimentary basin, was found in 1968 after gravity, magnetic, and seismic surveys were conducted between 1963 and 1964. The reservoir includes the Guantao (Miocene) and Minghuazhen (Pliocene) geologic layers within a dome-shaped structure called an anticline. The Suizhong 36-1 Oil Field was discovered in 1987 and produces oil from Oligocene fluvial-deltaic and lacustrine sandstones. Oil spills have happened often in this area, with three spills reported in two months in 2011. In 2024, CNOOC found a new oilfield containing 100 million tons of oil in the Bohai Sea.

Tunnel crossing

In February 2011, China announced plans to build a road and rail tunnel across the Bohai Strait to connect the Liaodong and Shandong peninsulas. When completed, the tunnel would be 106 kilometers (66 miles) long, which is twice the length of the Channel Tunnel linking England and France. In July 2013, a revised plan was shared, proposing a tunnel 123 kilometers (76 miles) long between Dalian, Liaoning, and Yantai, Shandong. The idea was first suggested by officials in Yantai in 1992, but no clear plan was developed. By 2019, construction had not begun, and the estimated cost had risen to 300 billion yuan ($43 billion USD).