Rimmed by the Rockies’ craggy foothills eight miles outside of Fort Collins, Horsetooth Reservoir sits at an imposing 5,420 feet. In 2007, a nervous Sarah Thomas dove into its 72-degree waters for the Horsetooth 10K, her first long-distance swim in open water. Halfway across the reservoir, Thomas fell in love with the discipline. “As I got closer to the finish, I felt more and more elated,” says the 35-year-old Conifer resident. “I was dead tired when I got out, but I knew I’d found my niche.”

A decade later, the former collegiate swimmer is setting world records, most recently by becoming the first athlete to complete a century swim—at least 100 consecutive miles—this past August.

Driving back from Lake Powell, where Thomas set her first world record with an 80-mile swim in October 2016, the idea of attempting 100 miles surfaced. She began researching the country’s largest lakes as possible locations, eventually settling on Lake Champlain due to its massive size, fairly predictable wind patterns, and stock of potential escort boats.

After months of clocking 30 hours per week in the pool at Lakewood’s Carmody Recreation Center (and other bodies of water across the state), Thomas waded into the 72-degree water at the northern end of Lake Champlain at 8:30 a.m. on August 7. Escorted by a sailboat carrying 10 friends and family members, the swimmer gulped carbohydrates and protein supplements from a water bottle thrown to her every 30 minutes. (She couldn’t touch another person or boat, per the Marathon Swimmers Federation’s requirements for an unassisted swim.) By the time she returned to her starting point 67 hours and 16 minutes later, Thomas had swum through three sunsets and two sunrises. The swim broke the world record she’d set in Lake Powell by 24 miles.

And yet, Thomas isn’t done stretching the limits of marathon swimming. In fact, she’s begun preparing for her next challenge: an 84-mile, four-way crossing of the English Channel in 2019.

Longest Swims

September 2013: Lake Memphremagog, Vermont & Quebec; 50 miles
October 2016: Lake Powell, Arizona & Utah; 80 miles
August 2017: Lake Champlain, Vermont & New York; 104.6 miles