UPDATE: A new set of original film prints of dogs diving under water, from 1997, was recently uncovered by Business Insider.

EARLIER: You think you know what a dog looks like when it dives into a swimming pool to fetch a ball. And then you see these astonishing underwater images by photographer Seth Casteel: It's a startling frenzy of teeth, jowls, eyes and claws.

The near-weightless conditions, coupled with the drag of the water, do odd things to a dog. Lips go flying. Fur and ears lie flat. Eyelids are peeled back.

Most of all, they reveal the intense determination that dogs bring to having fun.

Casteel—a commercial photographer who has worked for dog toy company Kong, JW Pet Co., Animal Planet, and Nintendo—first started shooting dogs underwater about 18 months ago when he was asked to do a portrait of a King Charles spaniel who wouldn't stay out of his owner's pool.

Last week, a selection of the Californian's images went viral (as they say) and now he's getting calls from all over the world to do underwater pet portraits.