The Cayman Islands are one of the Caribbean's best dive destinations for one simple reason: good genetics. The three islands — Grand Cayman, Little Cayman and Cayman Brac — are the tips of an enormous undersea ridge that is the lip of an even more enormous undersea valley. Called the Cayman Trench, this where the North American and Caribbean tectonic plates — the basic sections of the earth's crust that support the continents — come together; the trench is more than 21,000 feet.
The Caymans sit on the north side of the trench, and deep-sea exploration shows that the north wall has almost no sediment on it. It's like the sheer, bald face of a mountain cliff. There are no rivers on Cayman to contribute run-off either. No sediment plus deep water equals fabulous diving. That doesn't mean you won't get a 75-foot day, but compared to your local quarry or even places like the north shore of Jamaica, that's still almost gin-clear. Water moving up the wall from the deep trench brings microscopic plankton with it. These provide a never-ending buffet for sponges and corals, both of which grow to giant proportions. They also feed lots of small critters, which attract even bigger creatures, including majestic eagle rays and even the occasional whale shark.
In Grand Cayman's famous West Bay, what starts as ankle-deep water at the beach drops to more than 6000 feet less than a half-mile out. There are numerous dive sites on the shallow side of this shelf, and many more on the seaward side of the cliff's face. West Bay is also home to the territorial capital, George Town, and was the first place to be explored by divers. Many of the most well-known sites are in the area or along the west wall. The island's north, south and east coasts have superb sites as well, though the east coast — exposed to the prevailing winds — tends to be a bit rougher.
Grand Cayman is the easiest of the three to reach, with multiple direct flights from major U.S. cities, but the "Sister Islands" are even more spectacular. Little Cayman's Bloody Bay wall and Stake Bay on Cayman Brac each offer multiple sites with vertical surfaces, plentiful coral and big critters.
The following sites are on the writer's "best of" agenda, but any "top list" for the Cayman Islands is bound to come up short by someone's estimation. The island government has an initiative called "Cayman 365," identifying a major dive site for each day of the year. That's not just marketing hype.
Bonnie's Arch: Named for photographer Bonnie Charles, who disappeared on the wall some years ago, this site is at the north end of West Bay. A gentle carpet of sea fans, gorgonians and tube sponges gradually rolls over the edge of the wall. The gently waving branches of the soft corals are shot through with the brilliant metallic blue flashes of chromis flitting about, while squirrel fish shelter in the shade of overhanging ledges. At about 70 feet, there's an arch of undercut coral that spans a sand chute. Arches this large are uncommon in the Caribbean — most collapse before they reach this size. The arch itself is mesmerizing, but take some time to poke around the base and say hi to variety of reef dwellers who hang around.
USS Kittiwake: The latest addition to Cayman's collection of wrecks, this is a former U.S. Navy submarine rescue vessel that was sunk in 2011. It took the Cayman Islands Tourism Association and their point person, Nancy Easterbrook, eight years to apply for and receive the donation of the vessel from the Navy, clean it of military gear and hazardous waste, and pass both U.S. and Cayman Islands environmental tests. The effort was well worth it. The 251-foot ship is sitting upright on a sandy bottom just 64 feet deep, meaning her smokestack is only a dozen feet below the surface. In preparing the wreck, care was taken to make much of the ship accessible to divers. Unlike accidental wrecks, hanging wires, bulkhead doors and other things that can snare or trap divers have been removed. Also, because the Kittiwake is in a marine preserve, there's none of the dangerous monofilament fishing line that decorates wrecks frequented by fishermen. Inside, you can swim though the rec room, mess hall, ironing room, workshop, the recompression chamber for the ship's divers as well as other spaces. Because it's shallow and the water is clear, the Kittiwake also makes a fascinating snorkel site.
Orange Canyon: This has been a favorite with visitors for decades. Descending through a fissure in the wall, you exit at about 100 feet. The walls are spotted with giant orange elephant-ear sponges, which give the site its name. The surrounding area is often swarmed by great schools of silversides that create flashes of sunlight when they turn in unison. Large tarpon are frequent visitors as well — their huge underslung jaws and steel-like scales making them look prehistoric.
Babylon: The north shore of Grand Cayman has it's own share of excellent dives, and one of the most well known is Babylon. The wall starts at about 40 feet, goes vertical for a spell, then turns into a series of cascades of plate coral below 100 feet. Big spotted eagle rays are frequent visitors, along with other open water species. There are abundant sponges and even black coral bushes. You can do this from a dive boat run by one of the north shore operators or as a shore dive, with the wall starting about 300 yards offshore. Cayman dive guides go to Babylon on their day off — it's that good. The north shore can be a bit rougher than West Bay, so check the weather before you head out. If you decide to shore dive, it's about an hour from the hotels in West Bay. It's not that far as the crow flies, but you have to drive around the south side of north sound, then up to the north shore. West Bay boat operators don't go to Babylon frequently — it takes a lot more fuel than hitting the sites just off the beach — but for a tip, one of the smaller operators might be willing.
Stingray City: This shallow, sandy site in North Sound is renowned for its mass of Southern stingrays who loiter about, waiting for divers to come feed them. The site is often mobbed by snorkel operators, especially when a cruise ship is in port, so if you're staying on shore, go on a day when the cruisers aren't in. Typically the divemaster arranges everyone in a circle in about 12 feet of water, then feeds the stingrays, leading them around so each diver has a chance to touch the big galoots as they fly by. Stingrays eat by sucking things up into their mouths, which are located on the underside just south of their snouts. If they decide to take a taste of your arm, it won't hurt but you will end up with a nice hickey. The dive has become so popular that it now has a suburb, Stingray City East.
From: http://experience.usatoday.com/caribbean/story/best-of-caribbean/2013/10/22/best-diving-sites-in-the-cayman-islands/3118389/ by Steve Blount Published on October 22, 2013