It was pitch dark. Her shoulders hurt. Her legs were like jelly.

When Emily von Jentzen finished a 30-mile swim in Montana’s Flathead Lake last July, swimming farther was the last thing on her mind.

The 2001 gradu

ate of Marysville-Pilchuck High School, now a 28-year-old attorney, accomplished two big goals last summer. She became the first woman to swim the length of Flathead, a personal challenge with an altruistic aim. She also raised $9,500 to help pay medical expenses for Karmyn Flanagan, a little girl battling leukemia.

After swimming Flathead, von Jentzen took a couple months off from rigorous training. With summer coming again, she said, “I knew I wanted to do something.”

Seeing a TV news story about another suffering child, 5-year-old Katelyn Roker, helped make up her mind.

“Another year, another swim!” That was the subject line of email I received last week from von Jentzen, who lives in Kalispell, Mont., and works for the Flathead County Attorney’s Office.

And what a swim — the 55-mile length of Lake Chelan.

On Aug. 31, accompanied by two pontoon boats, von Jentzen plans to get in the water at the north end of the deep and narrow lake. Stehekin, at the top of the lake, is accessible only by boat. Von Jentzen, a competitive swimmer in high school, will hop off the boat to Stehekin and touch shore before beginning her endurance test.

After what she figures will be about 28 hours in the water — wearing a wetsuit like she did during the Flathead swim — she expects to finish at a public beach in the town of Chelan the afternoon of Sept. 1. She’ll follow USA Swimming open water rules, which don’t allow touching the sides of a boat.

In her research, she found no record of anyone ever swimming the length of Chelan. She found a Guinness World Records listing for a 130-mile ocean swim. The English Channel, a well-known open swim, is at its narrowest about 21 miles.

On a visit to Chelan three weeks ago, she stopped at the Chelan Mirror newspaper and also met a man at a boat rental shop who had lived in town almost 50 years. No one she met had heard of a swimmer going the distance of the lake.

Her effort is less about the record books than it is about helping. Katelyn Roker, according to the Flathead Beacon newspaper, has been battling stage 4 neuroblastoma since early 2010. It’s a cancer that causes tumors to develop from nerve tissue.

“I can’t just sit here and not do anything,” von Jentzen said. “From things I learned last year, I can do a better fundraising campaign and train better.” She hopes to raise at least $10,000 for Katelyn, the daughter of Jaime and Brian Roker. The family lives in Kalispell, and Katelyn has two brothers.

Von Jentzen keeps in touch via Facebook with Katelyn’s mother and with the family of Karmyn Flanagan, the Missoula, Mont., girl helped by her swim last summer.

Katelyn and her mom are in New York, where the child is undergoing treatment at the Memorial Sloan-Kettering Cancer Center, von Jentzen said.

And Karmyn, now 4, “is still in treatment and doing great,” von Jentzen said. “All her hair is back, she has a full head of curls. She appears to be doing well.”

Lucian Wischik, 37, is involved in a group called Seattle Open Water Swimming that organizes swims in Lake Washington and Puget Sound.

“Fifty-five miles is incredible,” said Wischik, whose longest swim was 13 miles around Mercer Island. He believes distance swimming is as much a mental exercise as a physical test. “It’s such a solitary endeavor,” he said.

The Seattle man believes a cause helps keep a swimmer from giving up. In 2009, he did a charity swim from the San Juan Islands into Canadian waters to raise money for Doctors Without Borders.

“Most long-distance swims seem to be for charity,” he said. “For me, that was an important motivation.”

Von Jentzen wants to make a difference while she can.

“You never know how long you can do athletics. You never know if you’ll have an accident,” she said. “Right now, I’m at a point in my life, I’m single, I don’t have kids, I have the time to be selfish and to train.”

Selfish? Not the word I’d choose.

Julie Muhlstein: 425-339-3460, muhlstein@heraldnet.com.

How to help

Emily von Jentzen’s 55-mile Lake Chelan swim, planned for Aug. 31-Sept. 1, is a fundraiser to help pay medical expenses for 5-year-old Katelyn Roker, of Kalispell, Mont., who is battling stage 4 neuroblastoma. To learn more or donate, go to http://alakkeforkatelyn.blogspot.com.