Up to 80 people were rescued after they were swept out to sea during a charity swim to raise money for the Royal National Lifeboat Institution.
All the swimmers had been taking part in a 3.8 kilometres charity race around Joss Bay in Broadstairs on Sunday.
Dover Coastguards said they were called to the bay around 10.30 and spent two hours searching for all the missing swimmers.
Watch manager Gordon Wise told BBC Kent: “It could have potentially been a very serious event, a very serious problem.”
He added: “When we got down there we found that there was a number of swimmers that had gone out, I understand the numbers are in the high upper tens.
“In the end through a search between two inshore lifeboats, rescue boats, and some paddle boarders which were part of the event, all people were brought ashore and accounted for.
“It was a long job. It went on for nearly two hours.
“There are some bad tides that run along there, rip tiding. Especially at the moment we are coming up to some of the highest tides of the year.”