A crowd of people was trying to cross the Gros Ventre River in boats and on horseback after midnight Friday, in an annual rush to find antlers shed by elk in the Bridger-Teton National Forest.
One horse drowned in the frigid river, which was running higher and faster than usual because of early snowmelt.
A boat carrying five people started taking on water and then capsized, U.S. Fish and Wildlife Service officer David Bonham said. Three of the people made it ashore by clinging to the hard-sided vessel, while the other two were swept downstream.
One of the two eventually got to dry ground under a rocky cliff. He climbed up "about 5 feet and was stuck on the cliffs, and he couldn't climb any higher," Bonham said.
The fifth man crawled onto a gravel bar.
Grand Teton National Park rangers used a raft to rescue the boaters, who were wet and cold but mostly uninjured.
"Fortunately, it was almost a full moon," which helped give rescuers the light they needed to find the boaters, park spokeswoman Jackie Skaggs said.
The two boats that were swept away were found safe downriver.
Antler hunting is a popular pastime in some Western states. Many people do it because they enjoy the hunt and like to keep what they find as souvenirs. Others sell their haul to artists and craftsmen who use the antlers to make artwork, knives and furniture. Overseas, shed antlers are sold as health or food supplements.
In Wyoming, Grand Teton and the National Elk Refuge — where thousands of elk congregate each winter — are off-limits to antler hunters all year. But the adjacent Bridger-Teton forest allows them in starting at midnight May 1.
Each year, collectors arrive at the park early, wait for the closure to be lifted and make a mad dash for the forest. To get there, they must cross the Gros Ventre.
"It's like the Oklahoma land rush," Skaggs said.
This year, the early snowmelt has the river near the community of Kelly running at nearly 1,000 cubic feet per second. That's about double the average for May 1.
Bonham said an ambulance was on standby Friday, but two victims suffering from exposure said they did not need to go to a hospital.