Swimmers Shed Light On Warming Lake Superior With 24-Hour Open Water Relay Record

A group of six swimmers finished off a record marathon swim on Wednesday morning, having completed a 48-mile trek in Lake Superior, doing so without wetsuits no less.

Alternating every hour, the swimmers swam through the night to complete the swim in 23 and a half hours, marking the longest observed, documented swim in Lake Superior without wetsuits or artificial aids.

Swimmers Casey McGrath, Craig Collins, Seth Baetzold, Mike Miller, Jeff Everett and Karen Zemlin took on the swim in part to draw attention to the warming lake, which is regarded as one of the coldest large lakes in the world.

The swim began on Tuesday morning at Split Rock Lighthouse State Park in Two Harbors, Minn., and wrapped up at Canal Park in Duluth.

Zemlin, a 55-year-old native of Plymouth, Minn., has done numerous open water swims over the years, including successfully crossing the English Channel in 2019 after making an initial attempt in 2015. She said the group dealt with 3-5 foot swells, though they weren’t swimming against the waves which was critical to their completion.

“We got a little bit of a lot of things, but Superior didn’t beat us this day,” Zemlin said, according to Minnesota Public Radio (MPR) News.

Sometimes the waves washed over them, she added, which presented a big challenge. “You just have to have enough experience not to panic,” she said.

The water temperature stayed in the low 60s throughout the swim, climbing as high as 66 degrees Fahrenheit towards the end. While still cold, the lake was sub-60 degrees at this time as recently as 2019.

“It’s kind of bittersweet,” said McGrath, a 51-year-old native of Minneapolis. “It’s a cool experience that we were able to have, but really in some ways we shouldn’t have been able to do it, not without wetsuits anyway.”

Lake Superior Temperature, 1995-2022 Avg. Versus 2023

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“I feel like I’m noticing more 70-degree water than I would have,” said Zemlin. “And I feel like I have to go farther sometimes to get away from the 70-degree water because that’s too warm for my purposes.”

University of Minnesota Duluth Large Lakes Observatory Professor Jay Austin told MPR News that a big reason behind the increase in water temperature is warmer winters.

“The difference between a heavy ice year where people are out recreating on the ice and going visiting the ice caves, and a year with basically no open lake ice, can be due to differences in average winter air temperatures on the order of 4 to 5 degrees Fahrenheit,” Austin said.

He noted that due to things like upswelling, there will still be significant cold stretches in the lake, and there will still be colder winters, but things are trending in the warmer direction.

“There are going to be more and more warm years, where it’s reasonably comfortable to swim, and fewer and fewer of the cold years,” said Austin. “But it doesn’t mean the cold years are going away.”