Wet clouds of steam filled the air on a cold winter night at Riverdale Hot Springs near Preston, Idaho, all but obscuring close to a dozen soakers and swimmers enjoying the strange mix of frigid temperatures and hot water.

"It's hotter than a roasted hot dog!" exclaimed young Preston resident Treyson Lamb.

While it might seem strange to soak in natural hot spring pools in the dead of winter when temperatures often dip near zero at night, it is a popular enough activity that four venerable resorts on the Utah-Idaho border stay open year-round.

Crystal in Honeyville (north of Brigham City), Lava Hot Springs in the Idaho town of the same name, Downata (near Downey), Idaho, and Riverdale all take advantage of the hot mineral water bubbling up from the depths of the Wasatch Fault by staying open.

Folks who come from near and far -- many convinced that the mineral water possesses therapeutic qualities -- come to enjoy the experience.

"Winter is the only time I come here," said Matt Hull of Preston after a soak at Riverdale. "The cold air goes good with the hot water."

Sharon Quesenbery of Willard is a regular at Crystal because she said the hot water gets her whole body warm. Cody Tea of Brigham City said he enjoys the sensation of sitting in a hot pool where temperatures hover around 104 degrees and then getting out to roll in the snow.

Kelsey Smith of Salt Lake City often makes a day of driving to Lava Hot Springs' hot pools, which are operated as a state park. After buying some lottery tickets, she uses nose plugs and goggles to stretch in the hot water and work on her range of motion.

For Bruce Adams of Clearfield, coming to Crystal Hot Springs helps him relax and relieve stress.

"After a stressful week, I come here and get rejuvenated. The minerals in the water make me healthier and stronger. And they help me lose weight."

At Downata, the resort hosts arthritis classes from 8 a.m. to 10 a.m. Monday, Wednesday and Friday year round where people suffering from that disease can exercise and soak in the warm water.

Health professionals have debated the benefits of soaking in mineral baths for hundreds of years. There is even a term for it, called balneotherapy. Many visitors like "taking the waters" for both their physical and mental health. In the winter, for example, just being outdoors on a sunny but cold day can improve someone's mood.

Those who believe in mineral water benefits like the fact that the hot springs portions of these resorts are totally natural with no introduced chemicals such as chlorine (though that chemical is used for water slides and in some of the pools open only in the summer). Because all pools have constant flows of hot water mean that new water is constantly coming into the pools. At Lava, for example, the spring produces 2.5 million gallons of water over a 24-hour period. In a two-hour period, water is replaced and new.

The other draw of the hot springs is simpler: They are fun.

For example, Adam Nelson, the manager of Crystal Hot Springs, said many Boy Scout troops come to his resort, where he offers free winter camping to Scouts on a Friday, when the water slides heated by hot water going over copper coils are open.

Another interesting aspect of these four resorts is that almost all of them began their operations in the early 1900s. They retain some of that old-time feel. But all four of them have undergone improvements over the last decade or so. And all seem to be enjoying increased popularity.

"Attendance has increased over a 10-year period," said Bridget Losee, administrative assistant at Lava Hot Springs, where a new 20,000 gallon pool with slightly cooler temperatures recently opened. "Our hot pool use is up 33 percent. Part of that is the economy and some is due to our improvements. We have a new pool and dressing rooms. The draw is relaxation. This is a quiet, more downbeat place where you can get away from the busy hustle of big city life."

Darlene Downs, who manages Downata with her husband Brett, said the resort has come up with a number of promotions. The most popular is steak and soak nights that include a nice dinner and a soak in the pools. New cabins and yurts offer an added benefit, since Downey is not a tourist town. There is a sauna, massage room, tranquility room with fountains, a steam room and an entertainment center available for groups.

Ryan and Lori Cook took up ownership of Riverdale two years ago and worked to remodel the motel units, which include double jacuzzi tubs that use the hot mineral water from the nearby springs. The couple also worked on cleaning the pools and remodeling the office area.

At Crystal Hot Springs, the three smaller hot tubs were recently resurfaced and the biggest soaking pool was recently emptied for resurfacing.

Still, the four resorts retain their rural feel and remain true to their roots, giving visitors the chance to step back in time for a few hours while enjoying a form of recreation and relaxation that has been around for hundreds of years.

wharton@sltrib.com