Ellsworth police said a man stopped at Branch Lake in Maine last week to take the dog for a walk while the man's companion took photos of the lake.
When the man encountered another man with a larger dog, he put the Yorkshire terrier inside the cab of his pickup truck, police said.
While the truck owner was talking to the other dog owner, the Yorkshire terrier somehow knocked the truck into gear, it said.
When the owner's companion saw the vehicle sink, she swam and rescued the dog from the truck.
