UPDATE: After five days of searching, efforts to find Kim Crumbo at Shoshone Lake in Yellowstone National Park have transitioned from rescue to recovery. More here.
Crews are searching the shore and waters of Shoshone Lake in Yellowstone National Park for a missing backcountry camper.
Photos provided by the Park Service show a helicopter which is also helping in the search.
A Park spokeswoman says the helicopter was used to ferry a boat to the backcountry lake for use in the search.
74-year-old Kim Crumbo, a former National Park River Ranger and Navy Seal who served two tours in Vietnam is missing on the Lake which is notorious for its dangerous waters.
The body of his half-brother, 67-year-old Mark O'Neill, was found on the east shore of the lake Monday along with the canoe and some gear the men were using. Their campsite was found on the south shore of the lake.
A cause of death for O'Neill is yet to be determined by the Jackson, Wyoming coroner.
"We still don't know exactly what happened but we have heard from multiple people who were camping out there that week, that conditions were very, very rough on the lake. There was one person in particular who said he had been coming to the lake for years and years and this was the worst conditions he's ever seen,” said Ashton Hooker, a park spokeswoman.
Shoshone is the second largest lake in the park at about 13 square miles. It sits at 7,795 feet above sea level.
The Park Service says winds of 45 miles per hour and two-foot-high waves were present on the lake this week at a time when the men could have been on the water.
The cold waters of Shoshone Lake were measured at 55 degrees on the surface by park Rangers searching for Crumbo. If you capsize in the water of that temperature your estimated survival time is less than 30 minutes.
Hooker said, “Your muscles kind of go into shock and you lose control of them. So it makes it difficult to swim, so definitely not ideal conditions if you were to capsize or fall into the lake."
Crumbo, the missing man was an experienced white water Ranger in the Grand Canyon and co-founder of the Grand Canyon Wildlands Council. That group later merged with another to form Wild Arizona.
Drowning is the third leading cause of death in Yellowstone, and Shoshone Lake has claimed many victims. Drownings on Shoshone include incidents in 2007 and 2002. In 1994, a Park Ranger drowned in the lake while paddling across to warn campers of an approaching storm.
Hooker said the search will continue as long as it is possible to continue given the high altitude and remote site of the lake.
