Hawaii.

A mere mention of this popular vacation destination conjures up images of white sandy beaches, deep azure water, lush rain forests, and the aloha spirit of a native people renown for its gentleness and hospitality.

In a word, paradise.

This is the Hawaii known to millions of people who travel to the island chain in the middle of the Pacific – a spectacularly beautiful terrestrial oasis 2,500 miles west of Oregon, with nothing but sea water in between.

Less well known is another Hawaiian paradise, one that lies submerged in 80-degree water just a few feet from the beaches for which Hawaii is famous. This paradise is one of the few places on earth that is still largely unchanged by man. It is a destination that is unsurpassed for unspoiled natural beauty.

Just below the surface of Hawaiian waters is an immense world teaming with wildlife in every conceivable shape, size, and color. These creatures are everywhere. Some live under the sand on the ocean floor while others hide out in caves, caverns and lava tubes. Multitudes can be found attached to rocks, coral heads, and sunken ships while countless others drift aimlessly wherever the currents take them. Virtually all can be seen from arm’s length.

This immense undersea kingdom, surreal in its beauty, is revealed only to adventurers willing to take the ultimate plunge into what can be a hostile and unforgiving environment, scuba divers. Yet the rewards for those with the wherewithal to explore this amazing underwater world are well worth the effort. That is why Hawaii has become a sort of Mecca for scuba divers from around the globe.

Hawaii has earned this distinction, in part, because it is one of the most isolated places on the planet. As such, it is home to a large population of marine life that can be found nowhere else on earth. Approximately 25 percent of Hawaiian fish species are unique to the islands, according to John P. Hoover, author of the book, “Hawaii’s Fishes,” which notes that only Easter Island and the Red Sea have a comparable percentage of endemic species.

Hoover explains this phenomenon, saying, “The ancestors of Hawaii’s shore and reef fishes drifted in as larvae. Only species with long-lasting larval stages made it. Distance is a natural filter.”

The fact that divers can see so many fish that they can see only in Hawaii gives the islands a certain appeal in the diving community, particularly those who are acutely in tune with what they are looking at.

“Hawaii is a destination for an educated diver,” said Gui Garcia, a diver with more than 10,000 dives who has devoted most of his adult life to uncovering the secrets of the Pacific. Garcia, 38, is captain of the Kona Aggressor II, a liveaboard dive boat that takes divers to some of the remote dive sites that Hawaii has to offer.

From the Aggressor, divers can see many of the 680 fish species that inhabit Hawaiian waters. In spite of such diversity, this number is considerably less than at other world class dive sites. Micronesia, for example, has nearly twice that number. The Philippines has upward of 2,000. That is where the educated diver comes in.

“I compare diving in Hawaii to walking in a Japanese garden,” said Garcia. “It’s not just for jumping overboard and seeing lots of fish. Everything in Hawaii has meaning.”

Volcanoes, like isolation, have had a major influence on the development of Hawaiian aquatic life and are another big draw for the diving community. Hawaii is one of only a few locations on earth where divers can swim through lava tubes which once poured molten earth into the sea. These tubes are frequently covered with exotic corals and flourescent nudibranchs, small worm-like creatures that are highly prized by macro photographers. Lava tubes also provide cover for lobsters, frog fish, lion fish, sea turtles, and other unusual creatures.

The same volcanic action that created this underwater labyrinth of tubes, “swim throughs,” skylights and arches also covered the ocean floor in some places with massive fields of lava boulders. This is another phenomenon unique to Hawaii, which is home to the largest active volcano in the world.

In fact, the Hawaiian islands are the tops of a dramatic undersea mountain range stretching 1,500 miles from Kure Atoll in the northwest to the island of Hawaii in the south.

The effects of the volcanoes here cannot be understated. For example, the ocean around the islands gets real deep real fast, which increases the chances of seeing big fish or “pelagics,” including whale sharks, hammerhead sharks, marlin, ono, and mahi-mahi.

Neither can isolation, which makes for some of the clearest ocean water in the world. This is an important consideration for divers who are always looking for excellent “vis.” Visibility off the Kona Coast often exceeds 100 feet, which makes it some of the clearest ocean water on earth. By comparison, visibility at dive sites off the coast of Oregon and Washington rarely exceeds 30 feet. Such good visibility not only enhances the visual experience for recreational divers but is a huge benefit to underwater photographers, who are always coping with low light situations. Water clarity, like the large percentage of endemic marine species, is a product of Hawaii’s isolation in the middle of the Pacific. The nearest land mass, California, is 2,551 miles away. Japan is nearly 4,000. French Polynesia almost 3,000. Therefore the water is free of sediment associated with continental coast lines. It is also nearly 30 degrees warmer, making it free of the kind of algae which tends to cloud Pacific Northwest waters.

No diving adventure in the Hawaiian islands would be complete without seeing a manta ray. These cousins of the shark are among the largest fish in the ocean, weighing up to 3,000 pounds and measuring more than 20 feet across. They are also very unusual in appearance, with flattened bodies, great winglike pectoral fins, and a long tail. Several dive shops along the Kona Coast offer “manta dives” at night during which they set out big lights which attract mantas to feed on illuminated plankton. Divers who have participated in these events describe close encounters with these gentle giants as something akin to a religious experience, marveling over the grace with which they perform rolls and spins. These antics are frequently performed within inches of divers who position themselves around the lights on the ocean floor.

All of this adds up to a diving destination that is hard to beat, which explains why more than 200 dive-related businesses are currently operating in the islands.