The small border collie, called Fly, had gone into the water at Lepe beach in the New Forest on Tuesday afternoon.
Fly's owner Mark Cowing jumped in to try and save his pet but could not contend with strong currents and had to be helped to shore by a kayaker.
Mr Cowing, 55, who is from Hemel Hempstead, Hertfordshire, said: "We were literally playing on the shoreline when all of a sudden he took it in his head to swim to the Isle of Wight.
"When he got 20 or 30 feet out I had to strip off, down to my underpants, and go and rescue him.
"He disappeared out of sight so I presumed he drowned. I tried to wave for help but I thought I was a goner.
Luckily a gentleman of 71 came out in his kayak and dragged me to shore."
A coastguard helicopter found the struggling dog 200m (656ft) offshore and directed an RNLI crew to its aid.
After the ordeal the dog scoffed down four pouches of food and a pork pie and went to sleep .