Oei, 31, slammed broadside into a black bear when it wandered onto the race course Sunday. She went airborne, then slid on her back across the pavement.
She wasn't seriously injured and even finished the triathlon. The bear didn't seem to be hurt, either, scampering back into the woods.
But the unusual high-speed encounter is a dramatic example of what experts are seeing across the West as drought forces bears to forage farther for food while urban development pushes into formerly wild areas.
In North Dakota, a black bear was spotted roaming through a Grand Forks neighborhood earlier this month. Officials suspect it came from Minnesota, looking for new territory.
Oei said she was focusing on the paved trail in the Boulder Peak Triathlon, which draws more than 1,400 athletes to a course just three miles outside of Boulder. She spotted the bear out of the corner of her eye and knew in a flash she had no way to avoid it.
"I tried to slow down as much as I could but I pretty much broad-sided it. I couldn't believe that it happened," Oei told CBS News, as she recovers from scrapes and bruises. "Who hits a bear?"
Oei's encounter is the latest anecdotal evidence coming in from around the West this year: In Nevada, near Lake Tahoe, a bear climbed into a vintage convertible July 2 and snacked on pizza and beer as a crowd gathered. In Alaska, a bear charged a jogger in an Anchorage city park this month. In Colorado Springs, a woman last week came home to find a bear rummaging through her refrigerator.
Colorado Division of Wildlife biologist Jerry Apker said encounters are up and will likely become even more frequent next month when bears start packing on weight for the winter.
"By mid-August, they start shifting gears when they start feeding. They might be foraging 22 hours a day," he said.
Years of drought have narrowed food choices and forced bears to forage far from their habitat. The situation gets worse as development moves into traditional bear habitats, and newcomers unfamiliar with bears leave out improperly latched trash cans and other tempting treats.
"Once they get a food reward, they've got an incredible memory and they come back to it," Apker said.
Linda Masterson, author of "Living With Bears: A Practical Guide to Bear Country," said the animals are big eating machines that are always on the prowl for an easy meal.
"A normal Colorado bear may range five to 15 miles a day, roaming for food," she said. "They are not looking for people to eat, we are not on the bear menu, but people do have food sources that are just very attractive to bears."
Something as seemingly innocuous as a bird feeder is an easy, 12,000-calorie fast-food option for a bear, she said.
Authorities across the West try to relocate troublesome bears, but Apker said they have to protect human life and will euthanize bears that put people in danger. New Mexico has a "three strikes" policy. Officials trap and move a bear found in a populated area two times before killing it.
In Colorado, it's a "two strikes" policy. And some bears don't even get that first pass if they're aggressive or found in an extremely dangerous location, such as near a school, Apker said.
Alarmingly, he said, the increased encounters are coming even as bear populations in Colorado decline. He said biologists estimate the state has 10 percent to 25 percent fewer bears than in the mid-1990s, due to drought. That they are being seen so frequently highlights just how desperate for food the animals have become, he said.
Barry Siff, race director of the Boulder Peak Triathlon, said Oei's bear crash over the weekend is a first for the 15-year-old race.
"I was in the medical area when the call came in. They said, 'We have someone who just hit a bear.' We said, 'You mean a barrier?' They said, 'No, we mean a bear,' " Siff said. "Maybe what we'll do is mark that spot next year with a sign that says 'Bear Crossing.' "
"There were 1,600 athletes in the entire triathlon and to be that one woman that gets hit by the bear is pretty unbelievable," Oei told CBS News.