As the narrow window for attempting the challenging swim from Northern Ireland to Scotland opened last week, only one of three first individuals to attempt it was successful.
San Franciscan Catherine Breed, 26, finished in a time of just over 11 hours.
She set off from Donaghadee at 3:57am on Tuesday and reached the Scottish coastline near Portpatrick around 3pm.
Ms Breed said she had aimed to break the record of 9 hours, 35 minutes. However, the conditions turned the record attempt into a fight just to finish.
She said: “The plan was to go for three hours and then re-evaluate because we thought it was going to get better, so we went for three hours and Padraig [Mallon, of Infinity Channel Swimming, who guided her] said I think it’s going to get better, you just have to fight for it, the record.
“Then after a couple of hours of it not getting better, I realised I was going to have to fight to finish it.”
Ms Breed said she counted 150 lion’s mane jellyfish. “Everyone told me there’s no jellyfish in the channel right now because it’s so cold, but within 15 minutes I saw three of them below me and I panicked a little.
“I counted 150 lion’s mane but I only got stung once. I think that was because I wasn’t paying attention and put my arm through its tentacles, but it didn’t hurt much.”
Ms Breed said she is determined to return to break the record. “I trained so hard for a long time for this and I went into it hoping to get a record, but knowing it wasn’t guaranteed,” she said. “After doing the channel I feel like I could do it in the right conditions. I don’t want to just leave it sitting.”
Ms Breed said she has been swimming since the age of four and became a competitive high school swimmer before winning a scholarship to UC Berkeley and making it to Olympic team US trials.
“When I graduated I didn’t want to give up swimming, but I didn’t want to race in the pool anymore, so I joined an open water swim team in Sam Francisco.
“People told me I should start setting goals so I did Lake Tahoe and then I did the English Channel, and then stumbled on to this one.”
Two others who attempted the marathon swim last week were forced to turn back due to the challenging conditions, including the cold waters of around 11 degrees, strong currents and the large numbers of jellyfish.