Editor's note: This updates with additional details of incident, guide being discharged from hospital.

You wouldn't think with walls rising roughly a mile above you on either side that you'd get struck by lightning. But that happened the other day to a Colorado River guide in the bottom of Grand Canyon National Park.

The Arizona Raft Adventures guide wasn't struck directly by a bolt, but more likely was shocked by a discharge of electricity from the bolt, said Dennis Smoldt, the company's personnel manager.

"There were two birthdays on the trip that they were celebrating. The group was gathered around a table where they were doing a birthday cake," Mr. Smoldt said from his Flagstaff, Arizona, office. The assumption was that "the bolt hit the beach, and the wet sand was the conduit for the electricity," he added.

The incident happened Sunday evening while the group was camped at river mile 220. The Grand Canyon Regional Communications Center received a call shortly after 9 p.m. Sunday reporting that an Arizona Raft Adventures river guide "required medical attention as a result of a lightning strike," a park release said.

The guide was airlifted out of the canyon by an Arizona Department of Public Safety helicopter and taken to the University Medical Center in Las Vegas, Nevada, for treatment of associated injuries.

Mr. Smoldt said the guide was released from the hospital Tuesday afternoon without any lasting injuries.

"He's doing very well," he said.

While lightning strikes at the bottom of the canyon are rare, according to park officials, "backcountry users can help reduce risk by getting off the water as soon as thunder is heard and not stand in the river or other pools of water during a storm."

"Avoid seeking shelter near trees and bushes that rise above others and avoid cave entrances," they add. "If in an open area during a storm, it is recommend to assume the lightning position which will reduce the chances of getting a direct strike. Individuals should squat or ball up to be as low as possible, without lying flat on the ground. Wrap your arms around your legs, keep your feet together, and if possible use a sleeping pad or other insulated object to sit on; avoid sitting on backpacks with metal frames."

Park records show that serious injuries and fatalities have occurred in the past as a result of lightning strikes. Visitors to the park are reminded that if the sound of thunder follows a lightning flash within 30 seconds or less, they should seek shelter in a building or vehicle, or proceed to the nearest bus stop to get on a park shuttle.