Two boats carrying 21 people, including 18 students from a Kyoto high school, capsized Monday off Henoko, a contested U.S. military base relocation site on Okinawa’s southern island.

The incident occurred around 10 a.m. amid a high-wave advisory, though water conditions were not notably rough. All 21 were rescued, but a 17-year-old female student and the captain of the smaller Fukutsu boat were pronounced dead. Two others sustained non-life-threatening injuries.

The teenager was wearing a life jacket at the time of her death. Officials confirmed no collision occurred.

The Henoko site has long been a flashpoint in tensions between local residents and Tokyo over the U.S. Marine Corps Air Station Futenma relocation. Okinawa hosts about half of the 50,000 U.S. troops in Japan, fueling longstanding concerns over safety, noise, pollution, and crime linked to military bases.