Following the guideline her life depends on, a diver threads the needle through a stalagmite forest in Dan's Cave on Abaco Island. A single, misplaced fin kick can shatter mineral formations tens of thousands of years old.
Bacteria color the water at a depth of 30 to 36 feet in Sawmill Sink on Abaco. Here and in a colorless layer below, poisonous hydrogen sulfide gas is present. Divers move through it with all deliberate speed.
Veteran cave diver Brian Kakuk lifts a more than 3,000-year-old Cuban crocodile skull—an animal no longer found in the Bahamas—from sediment in Sawmill Sink. Nearly oxygen free, blue holes preserve bones intact.
In Stargate, a blue hole on Andros Island, divers illuminate North Passage.
"All of a sudden, it's got you," says photographer Wes Skiles of the "insanely dangerous" vortex in Chimney Blue Hole off Grand Bahama. Like a giant bathtub drain, it sucks down millions of gallons when the tide comes in. "It's like going over a waterfall—there's no escape." Keeping his distance, a diver sets up equipment to measure the whirlpool's flow rate.
From a protected cove on Long Island, Dean's Blue Hole—Earth's deepest known underwater cave—plunges more than 600 feet into darkness.
Resting casually on a ledge 80 feet down, free diver William Trubridge admires the yawning entrance of Dean's Blue Hole on Long Island. Trubridge holds the world record for a breath-holding free dive—a three-minute, 56-second odyssey in this Bahamian cave, to a depth of 311 feet.
In Sawmill Sink, expedition leader and anthropologist Kenny Broad descends through the bacterial layer on an exploratory dive.
Kenny Broad sinks into the toxic hydrogen sulfide layer in Sawmill Sink on Abaco Island. By studying bacteria that flourish in the oxygen-free water, scientists hope, among other things, to learn how simple life-forms can lead to more complex ones.
In lightless blue holes, animals like this inch-long Agostocaris cave shrimp don't need surface pigmentation. Only part of the shrimp's digestive system has color.
The remipede is a "living fossil" nearly unchanged for 300 million years. It kills its prey, primarily other crustaceans such as cave shrimps, with venom-injecting fangs.
In Garbage Hole on Grand Bahama, Kenny Broad squirms through a narrow section, spooling out a guideline for a safe return to the surface. Although tidal currents sweep litter into this offshore cave's deepest reaches, its walls teem with life, including bright red bryozoans; smooth, gray sponges; and bushy, stinging hydroids that can raise welts on exposed skin. For many cave divers, entering a previously unexplored passage—as Broad is doing here—is the holy grail.
The Cascade Room, some 80 feet beneath the surface, leads divers deeper into Dan's Cave on Abaco Island. Nearly seven miles of the cave have been explored since the mid-1990s.
Through a halo of dive lights, Kenny Broad ascends a deep shaft in Dan's Cave on Abaco. The site is one of the world's most spectacular inland underwater caves, thanks to its abundant mineral formations, from columns and curtains to calcite "soda straws" that can break at the touch of a fingertip.
Archaeologist Michael Pateman lifts a centuries-old Lucayan Indian skull from a gridded site 110 feet down in Sanctuary Blue Hole on Andros Island.
Brian Kakuk has an arsenal of offbeat tools for gathering samples. An inflatable lift bag brings a stalagmite to the surface to be studied for evidence of abrupt climate changes in the past.
Brian Kakuk uses a turkey baster to collect red dust blown from the Sahara in ancient times.
Amid a hanging forest of stalactites in Ralph's Cave on Abaco, Brian Kakuk shines his dive light on a translucent stalagmite. During periods of lower sea level, when caves were dry, stalagmites and stalactites grew and eventually joined to form columns.
His air bubbles forced down by the current in a blue hole on Abaco, Kenny Broad fights to the surface, a stalagmite under his arm. Divers must bring extra breathing gas when they'll have to struggle against a siphoning tide.
Tires and other debris have piled up in Garbage Hole on Grand Bahama. "You're swimming through people's drinking water and junk piles at the same time," Kenny Broad says. "It really drives home why we need to protect these places."
A diver's-eye view just below the surface reveals the jungled entrance of Ben's Cave in Lucayan National Park on Grand Bahama. Established in 1970, the park protects one of the longest inland underwater cave systems on Earth.
Kenny Broad and Brian Kakuk surface at dusk after multiple dives in Sawmill Sink, where they collected bacteria samples and fossils. "It's an alien world down there," says Broad, "that keeps pushing us beyond our dreams."
Fins blurred by the halocline—a thin layer where waters with different salinities meet—a diver negotiates the ornately decorated Cascade Room in Dan's Cave.