You don't know what beauty is until you've explored a vibrantly colored Australian coral reef containing 1,500 kinds of fish, and giant clams three feet long.
You don't know what fear is until you've been caught in an underwater avalanche.
You don't know what wonder is until you've come face to face with a month-old seal pup while swimming under the frozen surface of a Siberian lake.
That is what Rick Sammon of Croton-on-Hudson, N.Y., has learned during his years as an underwater photographer.
When Sammon travels, he takes his scuba diving gear and does his sightseeing in places where most people would never think to look. What he has found are lush and hauntingly beautiful worlds _ places where the fish are colored like butterflies and every crevice is teeming with an untold diversity of life.
"It is another world," he says. "You're in the fishes' realm. It's almost like being in outer space."
Though these aquatic environments have been seen by few human eyes and are only beginning to be explored, they already face destruction from human activities such as dynamite fishing and seaside development.
Eager to alert the public to the world's underwater treasures before they are lost forever, Sammon _ who worked for a decade at a New York advertising agency _ had an idea.
Recalling the famous Seven Wonders of the World _ which were named in the 2nd century B.C. by the writer Antipater of Sidon and included the Pyramids of Giza and the Colossus of Rhodes _ Sammon decided to establish his own list.
He gathered a distinguished group of marine scientists, environmentalists and explorers in one room for a day. The experts nominated 26 underwater sites they thought most spectacular and ecologically important. From those, they selected the top seven.
Sammon then photographed these spots, which span the globe. Among the seven spots are:
Lake Baikal in Russia. The deepest lake in the world, it measures 5,380 feet in depth.e
The Great Barrier Reef, which stretches for more than 1,200 miles along Australia's northeast coast.
The Belize Barrier Reef.
The Galapagos Archipelago.
The deep ocean vents throughout the world, where large numbers of animals manage to survive without sunlight.
The result of Sammon's work was his book Seven Underwater Wonders of the World, published last year.
The book contains scores of color photographs and an informative text written in a casual style. But it is meant to be more than a collection of pretty pictures.
"We hope the book will have a real conservation message," Sammon said. "The seven ancient wonders are all gone now, except for the pyramids _ and they're crumbling. We need to protect our underwater wonders now or they too will disappear."
The Seven Underwater Wonders project brought many new adventures. Sammon saw a huge variety of gorgeous creatures _ trumpetfish, parrotfish, butterflyfish, balloonfish, sea cucumbers and sea lilies.
He swam with playful dolphins at the Belize reef. In the Galapagos Archipelago, he encountered a whale shark, which, at lengths of up to 60 feet, is the largest fish in the sea.
Sammon said he finds the dives, which usually last an hour, almost meditative. The only sounds he hears underwater are his own air bubbles, the squeaks of dolphins, the grunts of fish, and the clicking noises made by shrimps.
But the business of taking photographs underwater can be tricky. Sammon is weighed down by an air tank; he must focus while looking through a mask; and he has to swim while he shoots. His subjects are often uncooperative, flitting away as suddenly as they appear. In fact, many of Sammon's best photographs were taken at night, when he was able to catch sleeping fish while they slowly drifted.
"You have to know what you're doing before you get in the water," Sammon said. "If you spend a lot of money going to a place like the Galapagos and then you open your camera and water leaks out, it's very disappointing."
When most people think of environmental treasures, they picture tropical rain forests or the African savannah, not coral reefs, Sammon said. "That's because we tend not to think about what we can't see."
But when reefs erode, islands flood. When fish are poisoned, human beings lose an important food source and many jobs.
Sammon has seen coral reefs shattered by dynamite fishing, a common practice in which explosives are used to stun fish and bring them to the surface for easy collection. In the Philippines, 75 percent of reefs have already been destroyed that way, he said.
UNDERWATER PANORAMA: Abundant sunlight creates a stunning visual on the reefs in the northern Red Sea, one of photographer Rick Sammon's favorite dive spots.