TOKYO — In a tragic incident on Monday, two boats overturned near Henoko, a contentious location for relocating a U.S. military base, situated off Okinawa, Japan’s southern island. The mishap involved 21 individuals who were tossed into the sea, resulting in two fatalities, according to local authorities.

The Japan Coast Guard reported that among those aboard were 18 students from a Kyoto high school. They were divided between two vessels, the Heiwa Maru, which carried 10 students, and the smaller Fukutsu, accommodating eight. The students were visiting Henoko as part of a peace education program.

Rescue teams from the Coast Guard managed to retrieve all 21 individuals from the water. However, a 17-year-old female student and the captain of the Fukutsu succumbed to their injuries, as confirmed by officials.

Two other individuals sustained injuries, but their conditions have been assessed as non-life-threatening.

Authorities are currently examining the circumstances that led to the boats capsizing.

The accident occurred approximately one kilometer (half a mile) east of Henoko.

A wave advisory was in place during the accident, but the water was not very rough, and there was no sign that the boats collided, officials said.

Persistent protests and lawsuits between Okinawa and Tokyo have held up the relocation plan of the U.S. Marine Corps Air Station Futenma from a crowded neighborhood on the island for nearly 30 years.

Henoko is a popular destination for activists opposing the relocation, but the students were not protesting, officials said.

Okinawa is home to about half of the 50,000 American troops stationed in Japan under the bilateral security pact.

Many Okinawans complain about the risks of accidents, noise, pollution, and crime associated with U.S. bases.