On a 34-degree day in the middle of winter, anglers jockeyed for the best spots on the frozen surface of Twin Lakes near Leadville.
Pickup trucks and snowmobiles crisscrossed the ice to clusters of tents and huts set up for a fishing tournament.
Under the ice, it was less crowded. Divers floated about in silence, with little of the hubbub found atop the ice.
Each winter, Divers Reef of Colorado Springs sponsors a weekend of ice diving at the high-altitude lakes. Some divers take the plunge to meet a requirement for certification. Others are there in search of new thrills.
"Why do we do it? It's like climbing a great mountain - we do it because it's there," said Jim Petrenas, dive instructor for Divers Reef.
"It's just one of those things - you want to see if you can do it. Any time there's ice involved, it's an extreme environment."
In many ways, diving in the icy lake is similar to diving in the ocean. The equipment is basically the same - air tanks with regulators, goggles, flippers. But cold-water divers wear dry suits - watertight garments that keep the body warm and dry under a layer of air - with hoods and gloves.
The only part of the body that isn't protected from the cold is just around the mouth.
The Twin Lakes divers started the weekend by cutting a hole large enough to allow three people to drop into the water through 2 feet of ice. Then they built a hut to offer protection from the wind.
Before jumping into the water, each diver hooked onto a bright yellow tether rope that snaked 100 feet out of the water and across the ice. The tether ropes are the most obvious difference between ice diving and the warm-water variety.
"The sport itself isn't any different than diving in the Caribbean," Petrenas said, "unless the diver's regulator freezes up."
When that happens, the air tank begins freeflowing, and a person's air supply can be rapidly depleted.
"That's when it gets risky and that's where the ropes come in."
Ice divers tug on the ropes to communicate with those on the surface. One tug means "I'm OK"; two means "give me more line"; three, "take the line in"; and four, "get me out right now."
Petrenas and the other instructors from Divers Reef run the dives seamlessly. They've been doing this for years and the scuba shop has offered diving instruction for nearly two decades.
Underwater Connection, the other dive shop in town, also offers a weekend of ice diving - this year at Lake San Isabel.
The strange world an ice diver experiences is part of the sport's appeal, says first-timer Terry Rogers of Pueblo.
After his first dive, just a few minutes long, a breathless Rogers changed out of his dry suit and said, "Well, I did that. Don't have to do that again."
But there's something enticing about ice diving. Minutes later, Rogers suited up again. "I can't pass this up," he said. "When I was down there, I only thought about coming up. My regulator was freezing over and I had trouble breathing. But now I'm ready to give it another try. I want to see what's down there."
On this partly cloudy day, there wasn't much to see. Divers went only about 20 feet down.
"We don't go too deep," Petrenas said. "It's too murky."
The deeper a diver goes, the colder it is. Breathing escalates and divers use more oxygen from their tanks.
Most divers handle the icy water without a problem. Still, a safety diver sits by the hole in the ice throughout each dive, never leaving while divers are in the water.
Under the ice, divers explore a silent world. On a sunny day, the ice looks like stained glass, Petrenas said. Other days, it glows blue or green as sunlight filters through.
Diver Kate Keeley wasn't treated to the stained-glass vision. Still, she was excited.
"This is something I would never have done a few years ago," Keeley said.
A writer from Colorado Springs, Keeley has applied for a National Science Foundation grant, and if her proposal is accepted she'll travel to Antarctica where she'll ice dive.
Keeley, author of "Molly Finn and the Seven Seas Fountain," is planning the Antarctica trip as part of her research for a book on mergirls.
The divers at Twin Lakes haven't reported any creature sightings (not even a trout), but Petrenas said they find ways to have fun under the ice.
"Sometimes, we'll take a snowboard down, put it on the ice and snowboard upside down."