They may be called whale sharks but there's nothing to fear encountering one of these giant fish in the ocean - so much so that tourists in northwestern Mexico can swim alongside them on organized tours.
"These are tropical animals, very gentle, that you can swim with, and which go along at a maximum eight kilometers (five miles) an hour," explained Fabricio Mujica, who handles these up-close sessions in La Paz Bay, in Mexico's Baja California.
Starting in October, when these massive creatures - Latin name Rhincodon typus - come close to shore, tourists converge on the area in boats carrying 10 people.
The whale part of the fish's name is a misnomer. They are indeed sharks, but the non-dangerous carpet shark type that feeds on small animals on the seabed. They are around nine meters (30 feet) long and weigh some nine tons.
As the boats get close, the engines are cut so as not to frighten the animals. Then the tourists slip into the water, following instructions from their guide.
"It's a species that is really sensitive to boats and noise. They have a highly developed sense of smell - they notice any sort of chemical product or oil and that makes them flee, which is good because it lets them survive," Mujica said.
One tourist, Eduardo Rodriguez, has returned a second time to float in the water next to these giants.
"It's an experience difficult to put into words.... It's really spectacular," he said.
These observation activities are regulated in Mexico by the environment ministry, which checks on groups getting too close and fines any boats not sticking to the rules designed to protect the whale sharks.