The 64-year-old swimmer appeared refreshed and invigorated less than 24 hours after she had arrived dazed and sunburned, with lips swollen, onto the shore at Key West.
Nyad, who completed the swim Monday afternoon on her fifth try, told a news conference that the biggest challenge of the 53-hour swim this time around was high winds and swallowing large amounts of seawater, which she said made her vomit continuously.
"It was rough stuff," she said.
Cracking jokes and gesturing energetically, Nyad heaped praise on the members of the team that accompanied her, from a young man who swam beside her and encouraged her to keep going, to a box jellyfish expert who kept an eye out for the deadly creatures that ruined her past attempts.
The stinging sea life that had plagued her four previous attempts to swim the Florida Straits failed to appear until the final hours of her journey. That left Nyad free to concentrate on defeating the elements and persevering until she could step on dry land.
To help her fight the jellyfish, Nyad wore a protective silicone mask that had bruised her mouth and a full-body "jellyfish suit" that weighed down her crawl strokes.
She was free, too, of the nagging demons that drove her to attempt the treacherous crossing five times. She tried three times in 2011 and 2012. Her first attempt was in 1978.
Asked what she would do to celebrate, Nyad said a party would begin at 7 p.m. Tuesday night "and I expect it to go 53 hours."
President Barack Obama was among a flurry of public officials and celebrities who tweeted congratulations. The president's tweet echoed the sentiment Nyad has repeated many times when faced with defeat: "Never give up on your dreams."
Nyad's doctor, Derek Covington of the University of Miami and Jackson Memorial Hospital, said the swimmer was healthy and would not need a long time to recover from dehydration, sunburn and the swelling in and around her mouth.
"She was incredible to watch the whole way through," he said.
Nyad leaped from the seawall of the Hemingway Marina into the warm waters off Havana on Saturday morning to begin swimming. She paused occasionally for nourishment, but never left the water until she reached the white sand beaches of the Keys and waded ashore.
The support team accompanying her had equipment that generated a faint electrical field around her, designed to keep sharks at bay. A boat also dragged a line in the water to help keep her on course as she kept up the strokes, hour after hour after hour. Along the way, her team said it spotted thunderstorms on the horizon and even reported on her blog that cruise ships made way for Nyad as she crossed busy ship lanes.
"I always thought she could do it given her internal energy, her mental and physical strength, her will of iron," Jose Miguel Diaz Escrich, the Hemingway Marina commodore who helped organize the Cuba side of Nyad's multiple attempts, said Monday after Nyad landed in Florida.
"More than the athletic feat, she wants to send a message of peace, love, friendship and happiness ... between the people of the United States and Cuba," he added.
Australian Susie Maroney successfully swam the Strait in 1997 with a shark cage, which besides protection from the predators, has a drafting effect that pulls a swimmer along.
In 2012, Australian Penny Palfrey swam 79 miles toward Florida without a cage before strong currents forced her to stop. This June, her countrywoman Chloe McCardel made it 11 hours and 14 miles before jellyfish stings ended her bid.
Nyad acknowledged on Tuesday that she was glad when McCardel didn't make it before she had had a chance to, but she did add, to laughter from her team, that "I didn't want her to get bitten by jellyfish or die or anything."
In 1978, Walter Poenisch, an Ohio baker, claimed to have made the swim using flippers and a snorkel. Critics say there was insufficient independent documentation to verify his claim.
Nyad first garnered national attention in 1975 when she swam the 28 miles around the island of Manhattan in just under eight hours. In 1979 she swam the 102 miles from North Bimini, Bahamas, to Juno Beach, Fla., in 27.5 hours.
Nyad is also an author of three books, a motivational speaker and has been a reporter and commentator for NPR.