(Tribune News Service) — A 74-year-old former Navy Seal has been missing in Yellowstone National Park for three weeks, rangers said.

Kim Crumbo left in September for a four-night camping trip in Yellowstone backcountry with his brother and hasn’t been seen since.

“The search … has continued for nearly three weeks using helicopters, boats, sonar technology and ground crews,” park rangers said in an Oct. 8 news release. “Current weather forecasts call for deteriorating conditions over the upcoming week, including snow and freezing temperatures.”

Park officials will continue to search for Crumbo as long as weather allows, but have begun scaling back the recovery effort.

Crumbo was reported missing Sept. 19 after he and his brother didn’t return from a camping trip, park officials said.

His brother, 67-year-old Mark O’Neill, was found dead a day later near Shoshone Lake, the park’s second-largest lake. He died from hypothermia, park officials said.

Shoshone Lake has an average temperature of about 48 degrees year round, according to the National Park Service. People could only survive in the water for about 30 minutes.

Crumbo was visiting the park from Ogden, Utah. Both O’Neill and Crumbo worked for the National Park Service, and Crumbo is a former Navy Seal, park officials said.

Authorities said they are conducting an investigation.

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