A small plane carrying four people crashed into shallow waters next to a remote coastal town in Alaska on Wednesday, killing everyone on board, according to officials.

The Piper PA-24 was heading for the airport in the small town of Seldovia after taking off from Anchorage, according to a statement from the Alaska Department of Public Safety. Seldovia’s airport is about 136 miles southwest of Anchorage.

Alaska State Troopers said they sent a crew by helicopter from Anchorage and troopers by boat to reach the scene.   

After it crashed, thew plane was submerged in about 15 feet of water in the Seldovia Slough near the shore, said Clint Johnson, the National Transportation Safety Board’s Alaska region chief. Troopers had to wait until the tide went out in order to reach it.

Troopers were able to get the bodies of the four adults out of the plane. They were being sent to the medical examiner’s office and their names won’t be released until next of kin are notified, according to the Department of Public Safety.

It wasn’t immediately clear what may have caused the crash.

The NTSB is investigating.

Republican Sen. Dan Sullivan, of Alaska, said he’ll be getting a briefing from the NTSB and Federal Aviation Administration as they attempt to figure out what went wrong.

“These tragedies are heartbreaking and unacceptable, which is why aviation safety and infrastructure in Alaska continue to be a top focus of mine,” he said in a post on Facebook.

Less than a week earlier, another plane crashed at a remote military site in western Alaska, killing all eight people on board. The aircraft had been making its second runway approach in heavy fog and its pilots couldn’t see the gravel airstrip, authorities said.