PHOENIX - A Colorado woman who completed a nearly 132-kilometre swim across Lake Powell in 56 hours said Friday the vast distance wasn't her biggest fear.

"I wasn't concerned about the distance. I had trained and worked for that part," Sarah Thomas told The Associated Press a day after completing what is believed to be a record-breaking marathon swim. "But how do you stay awake that long?"

Thomas, who was still in bed after sleeping nearly 12 hours, said she credits the "little bit of caffeine" in the liquid carbohydrate and electrolyte mixtures she consumed every 30 minutes during the swim.

The 34-year-old from Conifer didn't stop swimming or get out of the water the entire time, allowing her to qualify for a possible record for an unassisted marathon swim.

She had a team of 13 people with her who travelled by house boat and gave her food every half hour in the form of a water bottle tied to a cord.

Thomas swam mostly freestyle but occasionally switched to backstroke or breaststroke to loosen up. The gruelling swim made it difficult to walk afterward because her feet and body were so shaky.

Exhausted and hungry, her first post-swim meal wasn't until breakfast the next day.

"This morning my husband tracked me down an omelet and some hash browns. I have to say it was the best food I've had in my life," Thomas said.

Thomas had done six major marathon swims since 2010, including efforts in Lake Tahoe and the English Channel. But none were as long as her journey on Lake Powell along the Arizona-Utah border.

She initially planned to swim in the ocean off the California coast but decided a lake might be better and began a search for the right one.

"There are not a lot of lakes that are big enough and logistically make sense," she said.

She chose Lake Powell for its amenities and proximity to Colorado.

Her training consisted of at least 25 hours of swimming each week since April. At the peak, she averaged 80 kilometres a week.

She said she was able to commit the time to training partly due to being able to work from home in her job as a hospital recruiter.

The San Francisco-based Marathon Swimmers Federation will have the task of verifying Thomas' swim.

Co-founder Evan Morrison said two independent observers, who are well-known marathon swimmers as well, were present to see her swim.

"They have the knowledge and the credibility. It's not just Sarah asking her brother to come out and say 'Oh yeah, my sister did this,'" Morrison said.

A federation panel comprised of 16 members from the U.S. and other countries will review logs, GPS tracking data and any photos and video.

Morrison expects everything to pass muster, calling Thomas one of the most "well-respected and well-known swimmers" in recent years.

The current record holder for an unassisted solo, open-water swim is Australian swimmer Chloe McCardel. In October 2014, she swam 124 kilometres in the ocean in the Bahamas in a little over 41 hours.

Thomas' swim was in a body of water with no current impacting her.

"So, in one sense it's a different category," Morrison said. "In another sense, (131.6 kilometres) is longer than (124.4). If ratified, it will be the longest unassisted solo swim in any body of water."

Thomas has no plans for more marathons until the Cook Strait in 2018. In the meantime, she plans to just keep swimming. Distance, not speed, has always been the draw for her.

"I may not be the fastest but I'm happy to keep going and going," she said.

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AP reporter Josh Hoffner contributed to this report.

News from © The Associated Press, 2016