A missing backpacker's body has been recovered from the eastern shore of Shoshone Lake in Yellowstone National Park, but the man's half-brother still remains missing.

According to a news release, search and rescue crews located Mark O'Neill's body on Monday.

O'Neill and his half-brother, Kim Crumbo, were reported overdue by a family member on Sunday from their four-night backcountry trip to Shoshone Lake.

The same day, park crews located a vacant campsite with gear on the south side of Shoshone Lake along with a paddle, canoe, PFD and other personal belongings on the east shore of the lake. Crews found O'Neill's body Monday morning.

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Crumbo remains missing. Both O'Neill and Crumbo are retired National Park Service employees. Crumbo is additionally a former Navy SEAL.

The incident remains under investigation. The public is asked to maintain distance from any law enforcement personnel, equipment, vehicles and their related activity for "the safety of the public in this remote area and to protect the integrity of our work."

Shoshone Lake is Yellowstone's second-largest lake. It's located at the head of Lewis Reiver southwest of West Thumb.

Its average temperature is roughly 48 degrees Fahrenheit. Survival time at that temperature is estimated to be only 20 to 30 minutes in the water.