The Florida Keys has long been known as a haven for multitudes of fish. If you haven't visited the Keys in a while, it's a great time to return. The establishment of the Florida Keys National Marine Sanctuary and subsequent creation of Sanctuary Preservation Areas (SPAs), where fishing is restricted, have resulted in increased numbers of fish and marine life. Having traveled extensively on assignments throughout the Caribbean over the years, we've never encountered fish populations to match those in the Florida Keys. If your forte is underwater photography or just undersea wildlife observation, the Keys are the place to be. We chose the Florida Keys Dive Center to reintroduce us to these fabled waters and reefs. Conveniently located ocean-side just south of Tavernier Creek at mile marker 90.5 on the Overseas Highway, the operation's two boats easily reach the best sites from Key Largo to the north and Islamorada to the south with plenty of interesting spots on the numerous Keys in between. In operation since 1983, owner Tom Timmerman and his highly experienced staff will safely guide you not only to the area's popular and renowned dive sites, but to several of their own favorites. As a PADI 5 Star IDC Center, the Florida Keys Dive Center is firmly committed to the principle that a diver should leave with more education than when he or she arrived. ''Since you'll be diving great locations anyway, why not complete an advanced certification course in two or three days?'' Timmerman suggests. Special sites On our first dive, the bubbles cleared to reveal the immense wreckage of the Eagle beneath us. Sunk as an artificial reef 16 years ago off Islamorada, the ship rests on her starboard in 116 feet of crystalline Gulf Stream water. Two gigantic masts cloaked with marine life extend outward over the sandy bottom. On our way to the stern, we swam past cavernous cargo holds swarming with fish. The ship's bridge offered seemingly endless photo backdrops: stairwells, companionways and portholes. No dive boats were visible when we arrived at the day's second dive site, Captain Tom's Ledge. There was also no mooring buoy, as this site is among dozens of ''secret'' discoveries that Timmerman and his experienced captains have found over the years. These guys have been here forever and they certainly know how and where to take you far from the maddening crowds of the cattle boats. Captain Tom's Ledge features a mini-wall that begins at 40 feet and protrudes sharply into the blue Gulf Stream waters. This ledge plays host to the entire food chain, including several large groupers and thousands of schooling tropicals. For a dramatic finishing touch, an impressive loggerhead turtle parted a curtain of swirling jacks just before the end of the dive. Special sites like Captain Tom's Ledge are one of the reasons that the Florida Keys Dive Center welcomes back so many returning divers. After making two dives on the morning trip, we signed up for an afternoon excursion that was highlighted by a relaxing drift dive along Conch Wall. We marveled at the large barrel sponges and schools of quickly passing jacks. We couldn't get enough. And the staff of the Florida Keys Dive Center just kept right on smiling and offering more remarkable dive sites. The next few days were devoted to diving as much and often as our computers allowed. It was with much sadness that we packed our dive gear and made our way home, all the while eyeing the calendar to plan a return date.