Reston — When Jean Young of Reston bundled up for her Saturday walk with her dog Seamus around Lake Anne Saturday, Feb. 2, she was worried her down jacket, long underwear, wool hat and gloves might not provide enough protection from the 30- degree weather. Little did she know she would be encountering more than 100 people wearing even less.

“As I came around the bend near the big tower, I heard cheering, and figured there was maybe a live show with a few brave souls outside supporting some friends,” she said. “I certainly didn’t expect to see half-naked people jumping into the water.”

They might not all have been half naked, some were in costumes, some in formal wear, but the more than 100 people who jumped into Lake Anne’s 35-degree water Saturday were doing so for a good cause.

The lake was the site of the sixth annual Freezin’For A Reason Polar Bear Dip, which raised money for Camp Sunshine, a nonprofit that hosts families of children with life-threatening illnesses. Gail and Bill Toth of Vienna were first exposed to Camp Sunshine after visiting in 1996 with their daughter Jennifer, who was diagnosed with cancer at age 3. They founded the dip at Lake Anne in 2008.

Since then, more than 500 people have participated in the event, raising $232,700 for Camp Sunshine, which is located in Maine. This year’s goal was to raise $100,000, enough for 50 families from the Mid- Atlantic area to attend Camp Sunshine.

“Everyone told me before I jumped that the anticipation was the worst part, once I jumped in it would be fine,” said Derek Lee, who made his first jump this year. “They were wrong. Getting out of the water and walking all the way to the community center while you’re uncontrollably shaking was the worst part. But as I was freezing, I thought of the people we’re trying to help, and I figured every one of them goes through something worse.”

Jumpers started hitting the water just after 2 p.m. Many followed the dip’s tradition of wearing a costume. Vikings, gladiators, Transformers, baseball players and even Spider Man were among the participants. But in some cases, clothes did nothing more than retain the near-freezing water.

“My biggest mistake was wearing pants,” said Lydia Felter, a nursing student from the Penn School is Nursing who jumped along with several of her fellow students.

This year Topical Smoothie Café donated towels for the jumpers to get into as they left the water and scampered to the Reston Community Center Lake Anne to get warm and change.