Four people on a helicopter chartered by the Alaska Department of Natural Resources are unlikely to survive after it crashed into a remote lake, a federal transportation official said Sunday.

The fate of the four, including three state geographic survey employees, was «presumed fatal,» National Transportation Board spokesman Keith Holloway said by email.

The crash happened around 7 p.m. Thursday, according to the NTSB, which was investigating why it happened.

Efforts to recover wreckage and wreckage were planned at a large, remote lake 51 miles south-southwest of Utqiaġvik, Holloway said. The city claims to be the northernmost community in the United States.

An Alaska State Troopers spokesman said volunteers from the Alaska Diving Search, Rescue and Recovery Team were activated and were on their way to assist local crews, the North Slope Borough Search and Rescue Team, with recovery.

In a statement Friday, the state Department of Natural Resources said its three employees were conducting field work from the air when the helicopter crashed.

«DNR is praying for our employees and the pilot, their families and the DNR team,» the Department of Natural Resources said.

Anchorage’s NBC affiliate KTUU described the helicopter as a Bell 206L-4 operated by Maritime Helicopters in Homer.

Holloway of the NTSB said investigators would examine the recovered wreckage, request air traffic communications, view radar data, read weather reports and speak with potential witnesses.

The helicopter’s maintenance records and pilots’ medical records and flight history will also be requested, he said.

A National Weather Service weather station at the Wiley Post-Will Rogers Memorial Airport in Utqiaġvik reported fog from just before 4 p.m. to about 11 p.m. Thursday.