A 47-year-old Plymouth woman attempted to swim across the English Channel on Friday before abandoning the effort with a mile  to go due to hypothermia, according to an online tracker.

Karen Zemlin, who grew up in Mounds View and swam at Hamline University in St. Paul, traveled to England a couple of weeks ago for her final training push in the gray waters of the channel.

About half the swimmers who attempt the 21-mile swim don’t finish. The currents and cold water are difficult to overcome.

"She froze out in the last hour of the swim and could not push in that last mile through strong spring tides to get to shore, her husband, Tom Zemlin, said. "She gave it a very valiant effort, but we had to pull her from the water as extreme hypothermia had set in and she was not longer safe."

Early Friday, Karen Zemlin pulled on her Lycra swimsuit, covered herself in a protective mixture of Vaseline and lanolin, and set off from Dover, England, in the direction of Calais, France.

According to tracking data online, she went into the water at 7 a.m. local time. (Dover is six hours ahead of Minnesota time; Calais is seven.) She got out of the water more than 12 hours later, the tracker indicated.

Zemlin had hoped to finish in 12 to 14 hours. By 4 p.m. Minnesota time, the tracker indicated she had climbed aboard her companion boat and was headed back to Dover.

She was the second person in her family to attempt the channel. Zemlin’s father, 75-year-old Roger Bosveld, made an attempt in 2007. Facing 9-foot swells, the retired St. Paul math teacher and master swimmer abandoned the swim after 5 miles.

Zemlin made it considerably farther. To prepare, she had participated in multiple open-water contests, including the 28.5-mile swim around Manhattan Island last summer.

As required, she booked her boat captain and official two years in advance. She committed to the training, routinely swimming three hours a day with the Hopkins Masters Swim Club, staying in the water for three workouts while others came and went on the hour. Zemlin logged 15 to 25 miles a week in the pool before heading to work teaching autistic children.

Certified channel crossings have strict rules, among them a ban on devices to aid speed or buoyants such as fins, wet suits or paddles. A single swimsuit is allowed, as are a single cap and goggles. The swimmer cannot make physical contact with the boat, nor can boat passengers touch the swimmer except to pass food, drink and light sticks.

Zemlin’s husband, Tom, and her brother, Brian Bosveld, were to ride along in the boat for her swim, checking on her stroke counts. Zemlin had said she wanted to stay at 70 strokes per minute. If she dipped close to 50, it would be a sign of trouble.

Had she finished, she would have joined a club with just over 1,500 members.

Katy Dooley, who grew up in Minnesota and now lives in Austin, Texas, swam the channel successfully in 2012. She said the hardest part was swimming in the dark. Dooley, an accomplished open-water distance and pool swimmer, said Friday that she had friends who abandoned channel swims within a half mile of the finish because of fatigue and/or hypothermia. “I thought it would be hard, and it was even harder than I expected,” she said. “It is topsy-turvy water, and it is challenging.”


Twitter: @rochelleolson