Seemingly unaware of the small chorus of wolf whistles, Matthew Rooney slid off his forest green robe to adjust the turquoise bikini top underneath.

Rooney closed the robe and pulled up a rubber-duck-shaped inner tube around his hips.

The 40-year-old Lyons resident was readying himself for his first Polar Plunge at the Boulder Reservoir. Rooney was participating on behalf of the Longmont Humane Society, where he is a first-year board member.

More than 800 people — some whose wardrobe included items such as hot pants, Hawaiian shorts, Santa hats, lingerie and wigs — participated in the 26th iteration of the event Thursday where people jump into the cold reservoir waters on the first day of the year.

They also give donations to increase awareness about Alzheimer’s disease and raise money for research, support groups and education.

The event is the largest fundraiser for the Young Professionals Alzheimer’s Association of Colorado, which took the reigns in 2007 from the Boulder Polar Bear Club, said Seth Barnhill, chairman of the volunteer group. Barnhill’s group has members in their 20s and 30s who have had Alzheimer’s touch their personal lives or are passionate about finding a cure.

“In terms of a monetary effect, it’s huge,” he said of the event.

In 2008, the association raised $18,000 when 600 people participated in the plunge. The larger turnout on the first day of 2009 is most likely attributed to the temperature, he said.

The 50-plus-degree weather was practically balmy compared to 26 degrees the mercury hit last year.

And although the water — at 36 1/2 degrees — was warmer as well, by about 8 degrees, the faces of participants said it all: It was still shockingly cold.

This was the second year that Longmont resident Kevin Mooney, his wife and two children decided to brave the frigid reservoir water.

His strategy?

“Jump in head first,” he said. “You go and get it over with.”

After a dip in the water, Mary Freeman, 55, quickly trekked her way through the sand to immerse in the warm and soothing salvation of a hot tub. The relief was present on her and her four tub-mates’ faces.

“Exhilarating,” said Jill Wierzba, 23, of the plunge, as she soaked in the hot tub.

Just down the beach, Longmont Humane Society’s Rooney looked to make a similar dash to warmer waters.

“It was great,” he said. “It was really not as bad as you’d think.”