The Yellow Sea Dispute Between China and South Korea

In recent years, China has towed a decommissioned offshore oil-drilling rig and two giant octagonal steel cages into the sea between China and South Korea, saying that the structures were used as deep-sea fish farms in shared waters. But South Koreans fear that they are more than that and could be used to expand China’s military influence.

South Korea’s National Assembly formally took issue with the Chinese structures on Monday when its ocean and fisheries committee condemned them as “a threat to maritime safety,” in a resolution adopted with bipartisan support. Those fears were bolstered on Tuesday by a report from the Washington-based Center for Strategic and International Studies.

“While available information suggests that the platforms are genuinely focused on aquaculture, concerns that the platforms may be dual-use are not unfounded, given China’s track record in the South China Sea,” said the report, which used satellite imagery and other data to track the installations. Dual-use refers to a second potential use for military purposes.

“Even without further expansion, the platforms are likely already collecting data that could have value for undersea navigation and detection,” the report said.

South Koreans see striking parallels between the Chinese installations and what Beijing has done in the South China Sea. China initially built artificial islands there for civilian purposes, but they were gradually transformed into military outposts, leading to territorial disputes with countries including the Philippines and Vietnam.

The tensions creeping up around the Chinese platforms in the Yellow Sea — called the West Sea by Koreans — will likely become one of the first challenges faced by the government of President Lee Jae Myung, who took office this month. Mr. Lee has vowed to improve ties with Beijing while at the same time promising to strengthen his country’s alliance with Washington. Mr. Lee hopes to meet China’s top leader, Xi Jinping, during the Asia-Pacific Economic Cooperation summit in Gyeongju, South Korea, in November.