A major search and rescue operation was launched after dozens of people taking part in a charity swimming race had to be pulled from the sea, the Maritime and Coastguard Agency (MCA) said.
More than 130 swimmers got into difficulty off the coast of Southwold, in Suffolk, with initial reports that up to 90 people were missing, an MCA spokeswoman said. It was later revealed two swimmers, including a woman from the Kettering area, were unaccounted for despite rescue efforts. They were both later found unharmed.
Four lifeboats and a rescue helicopter were involved in the rescue, while two people were taken to Paget University Hospital in Great Yarmouth with suspected hypothermia.
An MCA spokeswoman said it was unclear how the swimmers got into trouble as weather conditions were fine but the water was "very cold". Some swimmers were rescued by lifeboat while a number of people swam to the shore themselves, she said.
Everyone pulled from the water was conscious and there were no reported fatalities, the spokeswoman added.
Eyewitnesses spoke of exhausted swimmers coming out of the sea and being wrapped in towels, while a lifeboat hut close to the pier was turned into a makeshift emergency centre. James Dawson told the Norwich Evening News: "It was really, really tough conditions and people were coming out of the water looking exhausted."
It was reported that the event, the Southwold Pier to Pub Swim, was organised in co-operation with Adnams of Southwold brewery. The swim was due to start at noon with the mile-long event ending with a visit to The Lord Nelson Pub.
Some 58 people were rescued from the sea by the lifeboat crew, the Royal National Lifeboat Institution (RNLI) said. Lifeguards helped a further 27 people who were unable to continue swimming against the strong tide.
Simon Callaghan, helmsman at Southwold RNLI, said: "We were out on a regular Sunday exercise when we heard a swimmer calling for help. After that we had one of the busiest times I can remember, rescuing 58 people altogether. Our volunteer crew, the lifeguards and other rescue teams involved all responded brilliantly and may have averted what could have become a much more serous incident."
RNLI lifeguard supervisor Jo Thompson said: "Fortunately, all the swimmers are now accounted for. We had two lifeguards in the water on rescue boards, recovering people who became very cold and tired and so couldn't swim any further and also escorting other people out of the water and back to the beach."