St. Lawrence River

Called the "Caribbean of the North," the area around the Thousand Islands near the mouth of Lake Ontario is overlooked because freshwater dives don’t have the variety of marine life found in saltwater conditions. But the St. Lawrence River holds hundreds of underwater wrecks—including schooners and paddlewheel boats dating from the mid-1800s—and freshwater preserves them better than saltwater does. Visibility tends to hover around 40 feet but can worsen, depending on weather.

When to go: Water temperatures in the summer can get up to 70°F. Available from $80 per day via Action Scuba in Montreal, which includes all the necessary gear for two dives.

Palau

At a site known as the "Underwater Serengeti," you would expect some of the most varied and impressive marine life in the world, courtesy of the three ocean currents that converge. But Palau is also an excellent wreck diving destination: Air raids during World War II sank many U.S. and Japanese aircraft and vessels, such as Fujisawa Maru, a former cargo ship. And there’s Chandelier Cave, a cavern with swimming breaks in four chambers that provide air pockets. Perhaps the biggest draw is a landlocked lake and snorkel site filled with nearly 2 million non-stinging jellyfish.

When to go: any time. The water temperature remains in the low 80s°F all year. Air temperatures range from 75°F to 90°F, but sea breezes keep the humidity at bay. Parts of Micronesia rest in the typhoon belt, with storms most frequent from August to December. Available from $6,064 via Dive Worldwide, including flights, transfers, seven nights on the live-aboard ship, four nights at a resort on land, and one night in Manila.

The Red Sea

Equidistant from Saudi Arabia and Egypt are Brothers Islands and the Daedalus reef, each a beacon in the middle of the sea for all kinds of marine life. At Brothers, you could see 30 to 40 hammerheads, then find schools of manta rays in shallower waters, followed by oceanic white tip sharks. If you're lucky, you'll encounter thresher sharks, great reef sharks, tuna, and whale sharks among the sheer drop-offs that surround the reef. There are also two ancient wrecks at a 75-degree angle against the reef wall, both heavily encrusted in coral. Though the question mark here is political stability, the divers we spoke to have no qualms about visiting. 

When to go: Diving is undertaken year-round, though winds that make travel difficult mark December to March as the low season. At Daedalus, hammerheads are best from July to September, while oceanic whitetip sharks dominate in October and November. Available from $650, via Blue 02, which also offers custom trips, though larger groups should book 12 months to 18 months in advance.

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St. Lucia

The twin volcanic spires of the Piton Mountains, surrounded by miles of unspoiled rainforest, make St. Lucia a nature lover’s paradise. Underwater pinnacles are covered by coral, sponges, and gorgonians in an array of colors. French Angelfish, chromis, frogfish, and Sergeant Majors are other key specimens to look for as colorful long snout seahorses and hawksbill turtles swim leisurely along Anse Chastanet, a shallow reef popular among divers and snorkelers. The 165-foot freighter Lesleen M, purposely sunk in 1986, is covered in soft coral and sponges.

When to go: Diving is great all year. The water ranges from high 70°F in winter to the low 80s°F in summer. Trade winds provide cooling breezes most of the year, with average daytime temperatures in the 80s°F throughout the year. Rainy season runs from June to September, the Caribbean’s hurricane season. Two dives at the marine park are available from $100 via all-inclusive resort Rendezvous, from $515 per person, per night, and there are multiple 5-star PADI dive shops nearby. 

Indonesia

Lembeh Straits and Raja Ampat are Indonesia's most popular diving destinations and for good reason. The Lembeh Sea Dragon is a unique inhabitant of the straits—along with mandarinfish, hairy frogfish, stargazers, flamboyant cuttlefish, mimic octopus, and seahorse. Raja Ampat is the heart of the Coral Triangle, whose karst limestone formations and Boo Rocks formation, an underwater geological feature resembling the eye pits of a skull, make it a favorite for photographers.

When to go: For Lembeh, September and October generally offer the best diving conditions, though marine life is considered richest in July and August. When the rainy seasons strikes in January and February, some dive sites may close due to poor conditions. Available from $2,653 for a deluxe ocean-view cottage at Lembeh Resort, plus sessions at the resort’s underwater photography workshop. In Raja Ampat, diving is great year-round. Available from $5,900 on the live-aboard yacht The Arenui, a traditional wooden Indonesian Phinisi boat fitted with modern conveniences.

Fiji

The "soft coral capital of the world" has more than 390 coral species, plus 1,200 kinds of fish and five of the earth’s seven turtle species. With more than 330 islands and 520 smaller islets, this South Pacific archipelago has some of the best underwater volcanic topography—think caverns and swim-throughs, overhangs, tunnels, and sheer drop-offs dripping vibrantly colored soft corals.

When to go: Fiji has a warm, tropical climate most of the year, with air temperatures reaching lows of 65 degrees Fahrenheit at night and highs of 95°F during the day. The water temperature reads 75°F in winter and 85°F degrees in summer across the islands. Available from $3,195 through Aggressor Fleet, which will take you to Nigali Pass, Wakaya, and the Kadavu islands.

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