Superior Swimmers - Split Rock to Duluth

Split Rock Lighthouse State Park (Two Harbors, MN) to Lakewalk Beach (Duluth, MN)

71.5 km (44.4 miles)

23 hours, 32 minutes on 29-30 August 2023

Observed and documented by Kris Kulevsky and Tom Ringold



Team Members

Name Gender Nationality Age Resides
Karen Zemlin F USA 55 Plymouth, MN
Seth Baetzold M USA 28 Maplemood, MN
Michael D. Miller M USA 57 Minneapolis, MN
Jeff Everett M USA 62 Oakland, CA
William “Casey” McGrath M USA 51 Minneapolis, MN
Craig Collins M USA 64 Minneapolis, MN

Support Personnel


Kris Kulevsky
Masters swimmer and triathlete.

Tom Ringold
English Channel relay team member, 2010.

Escort Vessel

Swim Parameters

If water temperature at the start was 52 degrees Fahrenheit or lower, the swim leg duration would be 30 minutes for each swimmer for the first swim rotation, then 60 minutes for the remainder of the swim.

If a swimmer could not swim the complete duration of their swim leg and a successful early swim transition is made, then the swim may continue and the early-finishing swimmer sits out for the remainder of the swim.

Neither of these two exceptions were utilized on this swim. Each of the six swimmers swam four legs.

Multiple suits used by each swimmer, one at a time, complying with the swim-specific rules circulated publicly prior to the swim.

Three swimmers had nonstandard, non-performance enhancing GPS devices as disclosed in the rules prior to the swim. All other equipment complied with the swim-specific rules (textile suit, single latex or silicone swim cap, goggles, ear plugs, basic chronometer, glow sticks, button light)

Route Definition

  • Body of Water: Lake Superior (Minnesota, USA)
  • Route Type: one-way
  • Start Location: Rocky outcrop opposite Ellingson Island, Split Rock Lighthouse State Park (47.197864, -91.373941)
  • Finish Location: Lakewalk Beach (West Corner of the Lake) Duluth, MN (46.787064, -92.093740)
  • Minimum Route Distance: 71.5 km (44.4 miles)

Route Overview

Zoomed-in images of route: 1, 2, 3, 4, 5.

Coordinates for start, finish, and intermediate waypoints to determine the minimum distance enforced route of 71.5 km:

  1. (47.197864, -91.373941) Start: Rocky outcrop opposite Ellingson Island, Split Rock Lighthouse State Park
  2. (47.195650, -91.374984) East edge of Ellingson Island
  3. (47.187824, -91.383284) Rocky shore east of Split Rock State Park (backpacking campsite BP2)
  4. (47.131283, -91.465746) Rocky outcrop, southwest of Gooseberry Falls and south of E. Castle Danger Road
  5. (47.026954, -91.637041) Rocky outcrop between Burlington Bay & Flood Bay near end of Rocky Point Road
  6. (46.943542, -91.778743) Knife River Marina breakwater
  7. (46.923910, -91.817245) Stony Point Peninsula, Duluth Township
  8. (46.787064, -92.093740) Finish: Lakewalk beach (West Corner of the Lake)


This is the only known unassisted and documented relay swim from Split Rock Lighthouse State Park to Duluth.

The only known unassisted and observed solo swims in western Lake Superior are the 20-mile (32 km) swims of pioneer Vicki Keith in 1988, and Paula Stephanson in 2007 from the Wisconsin shore to Two Harbors, MN as recorded by the Solo Swims of Ontario safety organization.

The only known unassisted and observed solo swims in eastern Lake Superior are the more recent 17.8-mile (28.7 km) swims of Marilyn Korzekwa in 2018 and Liz Fry in 2022 from Whitefish Point (Michigan) to Pancake Bay (Ontario), also recorded by the Solo Swims of Ontario safety organization.

Swim Data

  • Start: 29 August 2023, 07:59:00 (Central Daylight, America/Chicago, UTC-5).
  • Finish: 30 August 2023, 07:31:50
  • Elapsed: 23 hours, 32 minutes, 50 seconds.

Summary of Conditions

Feature Min Max
Water Temp (F) 62 66
Air Temp (F) 52 69
Wind (mph) 0 12

GPS Track

Trackpoint frequency: 30 minutes. Download raw data (CSV).

Click to expand map.

Speed Plot


August 29th

  • 06:24 AM Sunrise
  • 07:44 PM Moonrise (95% Full)
  • 07:53 PM Sunset
  • 08:25 PM End civil twilight
  • 09:03 PM End nautical twilight

August 30th

  • 05:15 AM Start nautical twilight
  • 05:27 AM Moonset
  • 05:53 AM Start civil twilight
  • 06:25 AM Sunrise

Observer Log

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by Michael Miller

The Originators for this relay swim were Tracy Fredin and Beth Peterson. Beth co-led the effort with Connie Carlin through December of 2022, followed by subsequent co-leads Seth Baetzold and Mike Miller and team swim captain Karen Zemlin for the time period January through August of 2023.

Tracy is an outdoor enthusiast as well as the Director of the Center for Global Environmental Education at Hamline University in St. Paul, MN. Beth, a friend of Tracy’s, was inspired to launch this swim due to her past swim adventures on Lake Superior in the Apostle Island National Lakeshore where she swam island-to-island supported by Paul Voge on kayak.

Environmental awareness was part of the plan from the first concept of this relay swim, to engage the public to connect with the lake in a new way, and to highlight the climatic changes in the region around Lake Superior. Through a collaboration between the relay swim group and the Center for Global Environmental Education at Hamline University (St. Paul, MN) the swim event itself will be part of the documentary entitled “A Sea Change for Lake Superior”, under co-production between the Center and with the public broadcast station PBS North, with a planned release date of December 2023. The Center for Global Environmental Education was co-founded by polar explorer Will Steger in 1990, and the Center continues to foster environmental literacy and stewardship in individuals of all ages.

Only four unassisted solo marathon swims are on record for Lake Superior; Marilyn Korzekwa and Liz Fry from Michigan to Ontario, and Vicki Keith and Paula Stephanson from Wisconsin to Minnesota, as noted in the Recorded Swims found on the Solo Swims of Ontario website.

Climate change in the northern region of the Great Lakes (Superior, Michigan, Huron, Ontario, Erie) over the last four decades has resulted in an increase of approximately 4 to 5 degrees Fahrenheit for the summer surface water temperatures of Lake Superior. Winters are not as cold as the once were, and the amount of ice coverage of Lake Superior has trended lower. This allows the lake to stratify earlier and warm up the surface waters, due to additional days of solar gain in the spring time.

Climate change has resulted in more weather volatility in the region, and the swim region along the Minnesota shoreline is subject to 40-degree Fahrenheit upwelled waters when sustained westerly winds above 12 mph are encountered. The University of Minnesota Duluth Large Lakes Observatory maintains observation buoys and provides annual data for water temperatures one mile and ten miles offshore from McQuade Safe Harbor. This provides a good representation of the water conditions along the Minnesota shoreline of the lake.

With respect to the late summer surface water temperatures, the lake is preconditioned by the previous winter. The low ice coverage (maximum coverage of only 20% for the winter of 2022-2023) suggested that August 2023 surface water temperatures would be suitable for a relay swim.

There will likely continue to be high ice coverage years as there was in 2014-2015 (89%) and 2018-2019 (81%) in which the late August surface water temperatures the following summer were only 56 degrees and 47 degrees Fahrenheit respectively, but scientists cite statistically significant data for the decrease of ice coverage of Lake Superior since the 1970’s.

As the highest-latitude Great Lake, Superior is the last to stratify – a slow process to reach approximately 40 degrees Fahrenheit before a more rapid subsequent surface layer warm up occurs – so the available swim window is short each summer season.

The nearshore and offshore wind and water temperature historical data shows periods of time where upwelling occurred rapidly, and that it would extend many miles offshore. Our swim rules included an exception for the relay such that our first swim rotation would be 30 minutes instead of 60 minutes if the starting nearshore water temperature was 54 degrees Fahrenheit or lower. Fortunately, we didn’t have to exercise that exception; the winds for the days prior to the swim were from the northeast, which held the warmer surface waters along the shoreline, resulting in starting water temperatures in the low 60’s.

It was more desirable to include the exception in the rules versus the potential need to put on wetsuits; the general public has seen surfers in wetsuits in the winter when the surf is at its best. The effectiveness of our awareness campaign of the warming summer surface water temperatures would have been ‘watered down’ if we didn’t bare some skin for this swim and swim it in the traditional unassisted way.

The short seasonal time window for swimming Lake Superior can be summarized as the period of time from ‘tolerably warm enough to swim’ until ‘too windy to swim’. The relay swim targeted the date of the full moon (August 30th) for the swim, but reached an agreement with the boat captains for allowing the option to start one day earlier, or one day later. The first of the three days was chosen with 24-hour advance notice. The decision was easy and had high confidence of being the best choice, due to a passing high-pressure system that would result in tailwinds on the first of those three days, and headwinds the following two days. It would have been impractical to mobilize the vessels to Duluth prior to the event and swim the route in reverse order. Drone footage of the flotilla of the final 30 minutes of the swim the following morning confirmed that the wind had shifted 180 degrees (to a head wind), as seen on the alpha flag on the trailing dive vessel.

The 95% full moon on the mostly cloudless night was a welcomed sight, but this swim in late August had greater likelihood of unsettled weather and higher winds. Advice from our boat captains is that weather is most favorable from late July to early August, but also that the weather has become more volatile. The recent addition of a similar advisory in the Solo Swims of Ontario Rules and Regulations (Revision 20 to that document made in 2019) confirms that sentiment for the Great Lakes region of increased weather instability in the latter half of August.

The estimated 24-hour duration for the length of this relay meant there was no way to avoid the middle to late afternoon winds of the lake which can be avoided on solo marathon swims of shorter distances by starting in the evening and finishing the following morning. From a cinematic perspective for the documentary, the start and the finish had ideal conditions for capturing the event via specially permitted drone footage on flat water in the early morning light.

The late afternoon high-frequency waves plus swells added a definite sense of adventure to the swim legs, especially when those waves reflected back to the swimmer from the side of the lead sailboat. The trailing dive vessel housing the swimmers had significant side to side movement from the waves for at least a three-hour period from 5:30-8:30 PM, and the side-by-side doors of the full-sized fridge started self-unloading its contents at one point.

The most challenging task for the lead sailboat was to match the swim pace for the downwind drift without sails. The knowledgeable captains employed multiple 5-gallon pails and one rectangular storage tub, connected with ropes and attached to the stern to create a storm drogue “water parachute”.

Swimmers, captains and crew practiced swim turnovers in late July utilizing the 15-hp Rigid Inflatable Boat equipped with rope ladders, but this contingency method wasn’t used during the relay swim event. There was increasing concern for swimmer boarding at the end of their swim leg, but the crew and an acting swim chief helped facilitate that safe transfer via the rear tube ladder and water access platform.

Nothing more elaborate than a warm drink was required for rewarming, but the decreasing distances covered by swim legs as the swim progressed indicate the detrimental effect of the wind and waves, as well as less than desirable amount of rest during the breaks from swimming, and the time commitment for sharing the role of rotating swim captain.

Credit for this relay swim (subject to ratification) includes the helpful dialogue with researchers from the University of Minnesota Duluth Large Lakes Observatory, meteorologists from the Duluth office of the National Weather Service, guidance from Dr Marilyn Korzekwa, President of the Solo Swims of Ontario, as well as the Rules and Regulations Manual from that organization; the Marathon Swimmers Federation’s rules, standards, and procedures; retired boat captain training instructor Ted Gephardt, numerous sailboat, fishing boat, and diving boat charter operators; Paul Voge, Matt Kania, and other great lakes kayakers; pool and open water swim coach extraordinaire and alternate swimmer for this event David Cameron, the captains and crew from Sol Treks, Sea Change Expeditions, and Sol Mates Boat Charters, the collaboration with the Center for Global Environmental Education at Hamline University and their director Tracy Fredin, assistant director John Shepard, and additional communications and support staff and videographer John Thain; our ground support crew members Beth Peterson, Connie Carlin, and Tom Zemlin; swim coach Suzie Dods and her February 2018 24-hr relay swim co-hosted at the South End Rowing Club and Dolphin club; the relay swimmers dedication and preparation including feedback from Jeff Everett of his relay experience for the 35 hour double crossing of the Farallon Channel in 2015, and the many other supporters for the production of the documentary “A Sea Change for Lake Superior”.


Click to enlarge.


Vimeo: A Sea Change for Superior: Entire Relay Swim - Join a group of world-class marathon swimmers as they set a new record for a relay swim in Lake Superior. The video is an excerpt from A Sea Change for Superior: The Warming of the World’s Largest Lake, a public television documentary co-produced by Hamline University’s Center for Global Environemental Education and PBS North.


View folder of articles

Appendix A: Swim Prospectus for Hamline University

Appendix B: Buoy Data