Ascending from Devil's Ear spring, I'm startled to see a killer whale (Orcinus orca) looming over me. Kicking swiftly, I dodge the beast and look up as a flotilla of teens drifts past on inner tubes, towing a variety of marine mammals in their wake.

Inflatable marine life must be reckoned with when you dive the freshwater caverns of Ginnie Springs, Florida's all-natural water park. Long before Seaworld got started, people were flocking to this complex of seven springs in the north Florida forest. While the cavern depths of four of those springs--Ginnie, Little Devil, Devil's Ear and Devil's Eye--belong exclusively to divers, we must share the surface with swimmers, canoeists and "tubers," all drawn to flowing water so clear that it's bottled as drinking water.

Easiest to explore is the main Ginnie cavern, a sloping limestone fissure that leads to a 60- by 70-foot ballroom. If you feel like you're being watched, look up. Local divers like to wedge themselves into crevices and hang like fruit bats in order to surprise newcomers.

A guideline leads to the end of the cavern, where divers get a lift by holding onto the metal grate that blocks the cave entrance to the spring's source. About 35 million gallons of water a day passes through the grate, and kicking against the flow will make you feel like a guppy trying to swim into a jacuzzi jet.

The constellation of smaller caverns in the Devil Spring run is located closer to the tannin-stained Santa Fe River. Little Devil, Devil's Ear and Devil's Eye are shallow enough (from about 20 to 50 feet deep), small enough and close enough to be explored on a single tank.

From the bottom of Little Devil and Devil's Eye, you can see clear through the water to watch branches sway in the breeze and swimmers flail about as if floating on air. Over in Devil's Ear, however, it's a different story. Located at the edge of the river, the clear water flowing out of the spring fights to push back the encroachment of coffee-colored river water and the swirling kaleidoscopic effect is both eerie and hypnotic.

From the bottom of Little Devil, you can see clear through the water and count the oak leaves overshadowing the cavern.

Dive In: Ginnie Springs

LOCATION: The Ginnie Springs complex is 15 miles west of Interstate 75 in central Florida, near the town of High Springs.

SEASON: Open year-round, seven days a week from 8 a.m. to midnight. The dive shop stops filling tanks at 7 p.m. Monday through Thursday, at 10 p.m. on Friday and Saturday and at 8 p.m. on Sunday. It costs $27 to dive. The park is often crowded on weekends and holidays--visit mid-week if you want to avoid the crowds.

PROFILE: The four diving caverns at Ginnie Springs reach a maximum depth of 60 feet. Explore the cavern area that's illuminated by light from the surface, but never advance any farther. Only certified cavern and cave divers can carry lights and advance beyond ambient light into the cave system.

WATER CONDITIONS: Year-round visibility is 100-plus feet and the water temperature is a consistent 72F.

DIVE OPERATOR: Ginnie Springs Dive Shop, (386) 454-7188, web: www.ginniespringsoutdoors.com