Mark Freeley, of East Setauket, was walking with his dog Storm when the pooch noticed something in the water in Port Jefferson Harbor.
Freeley filmed the entire event, calling "Good boy Storm. bring him in" to encourage his pet.
The video shows the dog swimming to shore while grabbing a large fawn in its mouth.
When he reached land, Freeley said Storm followed the fawn and laid next to it, nudging it.
But the ordeal wasn't over yet.
Freeley immediately called the Strong Island Animal Rescue League who arrived on the scene to assist with the ill animal.
A NY man and his dog are being credited for rescuing an exhausted fawn floating in Long Island Sound not just once, but twice. That began rescue round two.
The vet was able to get the fawn to her vehicle and is now being treated.
"The second rescue was a lot of anxiety", Floridia said. She ran about a mile on the beach to help.
The fawn, which was covered in ticks and suffered an eye injury, should make a full recovery.
"I think it was a great thing for its instincts to kick in, to go out there and rescue it", Floridia said of Storm.
The fawn is rescued at an area animal rescue until it can get back on its feet.