Then the 4-foot-long otter seized Mike's snout with its teeth and started to drag the fluffy, white dog into the lake.
Heather screamed for help.
As the otter pulled the dog under, a family friend grabbed a pole, jumped into a small boat and tried to rescue Mike. But the dog already was limp and floating away.
"The otter went under water," said Rick Wolf, 19. "Then it jumped on the back of the boat and started attacking my foot."
Heather, 13, and her sister Stephanie stood in the back yard, hysterical.
"The otter had his whole mouth around (Wolf's) shoe," said Heather.
Wolf, whose shoe was not penetrated by the otter's teeth, kicked and jabbed it with the stick. The otter swam over to Mike, grabbed the dog and glided off.
Wolf, the boyfriend of Heather's 17-year-old sister, was not injured.
The body of the dog, an American Eskimo, was found on the shore of the lake on Wednesday, a day after the attack.
Pasco Animal Control has placed a trap in the Davis' back yard on Vienna Lane, which borders a small lake in the Regency Park subdivision.
"Otters usually are not aggressive, they're usually a very shy animal," said Denise Hilton, Pasco Animal Control manager. The otter could be a mother trying to protect her litter, or it could be rabid, she said.
Either way, "I'm sure it was very traumatic for them to have their dog killed by this critter," Hilton said.
Otters are protected animals in Florida, but they can be killed if they destroy property, authorities said.
Attacks are highly unusual.
However, there have been a few incidents involving river otters, which are aquatic members of the weasel family.
In 1999 in Melbourne, an otter bit a man on his shin. Earlier this year in New Bedford, Mass., a police officer was bitten by a rabid otter.
In Florida, otters are usually found near fresh water. They eat mostly fish, but have been known to eat birds, snakes and insects.
The animals, which can look a lot like giant wet cats when they emerge from the water, are usually 3 to 4 feet long, and can weigh up to 25 pounds. Otters have webbed toes, short legs and a small, flat head.
The violent attack left local and state officials puzzled. "This is very bizarre behavior for an otter," said Jeff McGrady, a wildlife biologist with the Florida Fish and Wildlife Conservation Commission. "It sort of just left us scratching our heads."
Heather's father, John Davis, said the family got the dog, Mike, as a puppy, five years ago.
He was very fond of Heather, and slept on her bed at night. When she was a little girl, Heather used to dress the dog in hats and other funny clothes, he said.
"Mike was very gentle, not aggressive at all," said John Davis.
Davis said his neighbor had seen an otter in the lake several weeks ago.
"If they had said an alligator was in the lake, I might have been concerned," he said. "I never thought anything about an otter."
Florida Fish and Wildlife Conservation Commission
HABITAT: In Florida, usually found near fresh water. They live in burrows on water banks, often under the roots of trees.
DIET: They normally feed on animals such as crawfish and fish.
SIZE: Usually 3 to 4 feet long, weighing up to 25 pounds. Otters have webbed toes, short legs and a small, flat head.