Rescue Crews Search for Missing Ex Navy SEAL, 74, After Half Brother Found Dead by Yellowstone Lake

Facebook Kim Crumbo

The search continues for a former Navy SEAL whose half brother was found dead earlier this week after the pair failed to return home on time from a four-night trip to Yellowstone National Park.

On Monday, search and rescue teams located the body of Mark O'Neill, 67, on the east shore of Shoshone Lake, Yellowstone's second-largest lake, according to a release from the park. A cause of death for O'Neill was not released.

The previous day, after a family member notified the park that O'Neill and Kim Crumbo, 74, were missing, "park crews located a vacant campsite with gear on the south side of Shoshone Lake, as well as a canoe, paddle, PFD and other personal belongings on the east shore of the lake."

In an update on Wednesday, park officials said that the search for Crumbo "will continue for the next several days."

The incident remains under investigation.

Jacob W. Frank/NPS Shoshone Lake

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According to the park, the average temperature of Shoshone Lake is around 48 degrees Fahrenheit — and "survival time is estimated to be only 20 to 30 minutes in water."

Additionally, the park's website carries several warnings about boating on the east shore of the lake.

"Most days, winds on Shoshone Lake come from the southwest causing the east shore to be pummeled by 2-3 foot or larger waves making paddling difficult if not impossible and dangerous," reads one safety warning.

Noting that "winds and waves on Shoshone Lake can develop suddenly at any time," the park suggests that all open water crossings be undertaken before 10 a.m. in the morning, which is when winds typically pick up.

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In addition to being a former Navy SEAL, Crumbo spent 20 years working for the National Park Service at the Grand Canyon, according to the website for the Rewilding Institute, a conservation organization Crumbo worked with.

He was as a river ranger and wilderness coordinator for the National Park Service and served as a professional river guide for a decade. He is also a member of the Potawatomi Tribe.

"We are shocked by the news that former Wildlands Network staff member Kim Crumbo has been reported missing from a backpacking trip in Yellowstone National Park," the organization wrote in a message on Facebook. "We join the community in offering thoughts to his loved ones and hoping for his imminent and safe return."

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"We are hoping against hope that he defies the odds, again, and turns up alive, John Davis, the executive director of the Rewilding Institute, told The Salt Lake Tribune.

"If there was anybody who was going to figure out a way to survive in the wild, it would be Crumbo," added Katie Davis, executive director of Wildlands Network, where he previously worked as their Western conservation director.