The program welcomes both scuba certified divers as well as on the surface swimmers. Having recently gone through scuba training with my 16-year-old-son, we couldn't resist an afternoon jumping into the clear safe water to enounter more fish than we ever imagined--thousands and thousands of them.

I don't know who's more surprised, me or the 300-pound grouper eyeballing me. The 7-foot gray mass of bad temper obviously takes a minute to decide that I'm not trouble, so he warily swims away. We meet several more looming around during the 30-minute tour.

We follow our underwater leaders through the tank, pausing to see oddities such as the humphead wrasse, a green fish with a prominent forehead that looks like he escaped the Finding Nemo cartoon movie, 10-foot-long hammerhead sharks staring with wide blank eyes, and a pregnant bowmouth guitar fish, settling onto the sand with an uncomfortable looking swollen belly.

As we swim by the visitors viewing windows, we wave expertly to the regular guests. One of our swimmers has his family waiting inside, and we stop to pose for a photograph.

Wherever we wander in this gorgeous blue underwater zoo, we encounter huge schools of colorful residents--golden trevally flutter by like butterflies and crimson snapper look like an impressionist painting against the green rocks. Sawtooths settle onto the bottom with bizarre tool-like snouts. Dozens of rays with suede-like backs wave up and down as they swim.

The experience ends too quickly. Trying to get out of the tank, Trixie and Alice follow our movements. Their curiosity about us matches our own. We all agree that we would try to return another afternoon to dive here again.

The Journey With Gentle Giants program includes behind the scenes tours, a souvenir t-shirt and photograph of your swim, as well as a 30-minute immersion in the world's largest aquarium. Participants may scuba at 3 p.m. or swim at 4:30 p.m. daily. Reservations required. Cost: $190 for the swim, $290 for the dive program. www.georgiaaquarium.org.