A search is still underway for 76-year-old John Allen from Preston.
He was last seen entering the Ravenglass estuary, in Cumbria, at around 9am last Monday.
The Preston pensioner had been spotted swimming at Ravenglass estuary and Coastguards received a 999 call from a member of the public who reported seeing Mr Allen in the water attempting to swim across the estuary.
Police were called after concerns were raised for his safety.
Inspector Mark Wear, from Cumbria Police, said: “Following enquiries we do not believe Mr Allen was swimming in the estuary yesterday morning, but may have been trying to help his dog out of the water. The dog is fine, however Mr Allen has not been seen since.”
His dog made it back to shore and was barking for his owner.
Underwater search teams searched the estuary with more searches undertaken along the shoreline.
A hundred people joined the search and appeals went out to the local community to get in touch with any relevant information they may have.
Mr Allen is described as 5ft 8in tall, of slim build and bald. He was wearing a green fleece, green suede trousers and walking boots.
Paul Parkes, watch manager at Liverpool Coastguard, said: “We are currently coordinating a large-scale search and doing all we can to find this missing man.
“If anyone was in the area earlier this morning and has information on this swimmer, please call Liverpool Coastguard on 01519 313341.”
Anyone who may have seen Mr Allen should call police on 101 and ask for the duty sergeant at Whitehaven.