(NEW YORK) — The U.S. Coast Guard (USCG) said it’s investigating several deaths and injuries of U.S. citizens that took place on passenger vessels recently traveling in Antarctic waters.

The Coast Guard, the National Transportation Safety Board and other agencies from around the world are deploying teams to Ushuaia, Argentina to investigate four instances that took place between Nov. 15 and Dec. 1, 2022, the agency said.

“Our deepest sympathies go out to the families of those impacted by these tragedies,” Capt. Gretchen Bailey, the Coast Guard Activities Europe commanding officer, said in a statement. “We are proud to work alongside the NTSB and our international partners to investigate these incidents and make meaningful safety improvements for worldwide passenger vessel operations, especially in unique high-risk environments like the Antarctic.”

In one incident, two U.S. citizens died when an inflatable boat from the Portuguese-flagged passenger vessel, World Explorer, capsized with six passengers aboard near Elephant Island, Antarctica, the USCG said.

A U.S. citizen was injured when an inflatable boat from the Norwegian-flagged passenger vessel, Viking Polaris, sustained a keel-bladder failure near Damoy Point, Antarctica, according to the USCG.

One U.S. citizen died, and four others were injured in a third incident when the Viking Polaris was struck by a large wave in the Drake Passage while transiting to Ushuaia, Argentina, the USCG confirmed. Passengers on board the ship described choppy conditions leading up to the incident, which officials said was caused by a “rogue wave.”

A U.S. citizen died from “an injury sustained” aboard the Netherlands-flagged passenger vessel, Plancius, in a fourth incident, the U.S. Coast Guard.

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