Karen Zemlin at the start of her swim with Isle Royale behind her. Photos: LeAnne Johansen
A Plymouth swimmer receives recognition from the Marathon Swimmers Federation.
Karen Zemlin took on one of the most unpredictable stretches of Lake Superior, setting out from Isle Royale, Michigan, to Minnesota’s Pigeon Point on August 13, 2025. This swim has since earned her the 2025 Yudovin Award for Most Adventurous Swim, which was announced this month. “It’s exciting that this award brings the adventure of Lake Superior to the attention of the international marathon swimming community,” Zemlin says. “We can’t wait to see who will come and swim next.”
During her swim, what began as relatively manageable waters at 64 F suddenly shifted. Midway through the swim, a powerful upwelling pulled frigid waters to the surface, dropping temperatures to a chilling 46.9 F—one of the coldest ever recorded for a documented Marathon Swimmers Federation swim. Regardless, Zemlin pushed through the sudden change and reached the shore, completing an impressive 14.2-mile swim.
Karen Zemlin at Grand Portage harbor after her Lake Superior swim.
Zemlin’s Lake Superior crossing is just the latest feat in her career. She has completed the Triple Crown of Open Water Swimming by traversing the English Channel, the Catalina Channel and around Manhattan Island. Zemlin was also the first to complete a documented crossing through Lake Mille Lacs, among other remarkable swims across Minnesota. Building on that experience, she recently launched Superior Swims, a resource designed to help other athletes navigate the unique challenges of Lake Superior, from route planning to safety considerations.
We connected with Zemlin to learn more about her Lake Superior adventure and her plans for Superior Swims.
What gives you strength while you are in the midst of an intense swim?
My inner strength comes from years of experience, mindset and trusting myself and my crew. It never occurs to me to get out before the finish. It’s not thinking about why to get out; it’s thinking about the next thing to do to keep swimming. It is not thinking about where I hurt; it’s thinking about where I feel strong.
How did your Lake Superior swim feel different from the other iconic swims you’ve completed?
Every ultramarathon swim has unique challenges, and in Isle Royale, it was the extreme upwelling that dropped the water to a burning-cold 46 F. While the English Channel is a test of endurance against the tides and jellyfish, Isle Royale was a dramatic battle against the sudden, unpredictable nature of the world’s largest lake. That kind of temperature swing doesn’t happen in oceans.
How do you hope Superior Swims shapes the way athletes approach Lake Superior?
I hope Superior Swims serves as a living resource that draws international athletes to the lake prepared to take on the challenges with a sense of wonder. By documenting these routes, I want to create awareness of waters worthy of protection while proving that even its most intimidating reaches can be navigated with curiosity and a sense of adventure.
Marathon Swimmers Federation
Facebook: Marathon Swimmers Federation
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