Shoshone Lake is an attractive destination for paddlers, but it can be deadly/Kurt Repanshek file

A painstaking and heartbreaking recovery mission continued Saturday for a canoeist missing since last weekend in Yellowstone National Park's second largest lake.

Kim Crumbo, 74, of Ogden, Utah, and his half-brother, Mark O’Neill, 67, of Chimacum, Washington, were reported missing last Sunday by family members. The two retired National Park Service rangers had planned a four-night backcountry trip to Shoshone Lake, a 12.5-square-mile  lake with no road access.

Paddlers planning to visit Shoshone must first cross Lewis Lake, then follow the roughly 3-mile-long Lewis River Channel to Shoshone. Those who make the journey enjoy wilderness solitude and the Shoshone Geyser Basin on the lake's western shore.

But as picturesque as Shoshone Lake can be, it can be equally dangerous and unforgiving. Afternoon winds can whip the lake and generate 3-4-foot and larger waves that challenge the best of paddlers. Back in 1994 the lake claimed a backcountry ranger who capsized in his kayak. In 2002, a 39-year-old Idaho man, David Graham, of Chubbuck, and his 12-year-old son, Quinn, died after their canoe overturned.

With water temperatures that average 48 degrees Fahrenheit year-round, survival time in Shoshone Lake is estimated at only 20-30 minutes.

After the two men were reported missing last Sunday park rangers located a vacant campsite with gear on the lake's south shore, as well as a canoe, paddle, PFD, and other personal belongings on the east shore of the lake. The next day O’Neill's body was found along the east shore.

Over the past five days the National Park Service has used ground teams, aerial spotters, and searchers on rubber Zodiac-type watercraft in the search for Crumbo, said Yellowstone Superintendent Cam Sholly. Sonar equipment also was being used, and divers were on standby.

"This is an incredible tragedy," Sholly said Saturday. "Mark and Kim were well known and highly respected rangers in the NPS. We're in very close contact with the families of both men who are working through the pain of these losses."

Crumbo had been a Navy Seal before his Park Service career and had two tours of Vietnam during the war. Part of his 20-year NPS career was spent at Grand Canyon National Park, where he was a river ranger and later the park's wilderness coordinator, according to his biography at the Rewilding Institute, where he was a board member.

On Friday the park announced that the search had turned into a recovery mission.