The dorsal fin surfaced in the boat's wake, but the rising figure seemed too big to be a dolphin.
The orca whales leaped out of the water, prompting two Lutz residents to snatch their cameras and watch as the mammoth creatures frolicked in the waves.
Laura and Rich Howard, who run the marine photography site oceansofimages.com, have since had their encounter in the Sea of Cortez featured on the Today show, NBC News and several other television stations.
The couple had been diving moments before, snapping photos of curious sea lions, when the captain ushered them back on the boat. It seemed too soon, they thought.
Then, they realized a pod of about 20 orcas was playing around their boat, Rich Howard said.
Orca whales have become well-known through theme parks, such as Shamu at SeaWorld, and movies, such as Free Willy. Orcas, also called killer whales, are among the sea's most effective hunters and sometimes go after other whales as prey.
"The reputation they have as killers is definitely real," Rich Howard said. "But I don't think that's all they're all about. They're very social and everything social wants to have fun."
The Howards got a front-row seat to the spectacle. They said the orcas traded off every few minutes to give all of the whales in their pod a turn.
"It's like they were waiting in line at Busch Gardens," Laura Howard said.