Senior US distance swimmer Diana Nyad was "struggling" but fighting on Saturday in her daring third bid to cross the sea from Cuba to Florida, according to a post on her blog.
The 62-year-old, who is seeking to become the first person to make the 160 kilometers (100 miles) swim without a shark cage, was weakened by a series of jellyfish stings after starting her journey on Friday night.
"She is struggling right now. Her usual stroke pace, between 52 and 55 strokes per minute, has dropped to 48, but she is able to swim," said a post titled: "A Challenging Night."
"At 5:50 am Diana stopped her freestyle stroke and complained that she couldn't breathe properly, that she wasn't getting oxygen to her muscles," the post said.
Two doctors from the University of Miami administered the veteran swimmer with prednisone, an anti-inflammatory drug, along with oxygen and other medication.
"Diana treaded water between 7 am and 8 am, and said she felt better, but still couldn't get enough oxygen to her muscles," the blog added.
Nyad failed on two previous bids, in 1978 and last month, in her quest to swim across the treacherous Florida Straits from Havana to Key West, Florida.
"You're doing better. I can see it," Bonnie Stoll, her chief handler, was quoted as saying on Nyad's blog, which said the swimmer was 25 kilometers off the Cuban coast.
Shoulder pain, asthma and ocean swells hobbled Nyad's August attempt.
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