LAKE HURON, MICHIGAN
Thunder Bay Divers, (517) 356-9336
What was once a ship captain's nightmare - some 160 vessels may lie at the bottom of Lake Huron's Thunder Bay - is now a wreck diver's dream. Known wrecks are scattered in water as shallow as 12 feet and as deep as 180 feet, making this a playground for all diving skills. As added enticement for the adventurous, plenty of wrecks remain undiscovered. More good news, last June the U.S. government decreed Thunder Bay the country's first freshwater national marine sanctuary, a protective status that ensures no pilfering. So wrecks like the Grecian, a steamer split in half by a vicious 1906 storm, will forever remain eerily intact.

FLOWER GARDEN BANKS, GULF OF MEXICO
Flower Garden Banks National Marine Sanctuary, (979) 779-2705, www.flowergarden.nos.noaa.gov
If you must turn to the sea, turn here. Drive an hour south of Houston, then head 100 miles out into the Gulf of Mexico, to the world's northernmost reef. Two salt domes bump up off the ocean floor, smothered with spectacular corals and sponges, and swept by huge mantas, hammerhead sharks, loggerhead turtles, and a Jackson Pollock explosion of tropical fish.

THE CHUTE, ARIZONA
Drew's Dam Divers, www.damdivers.com
Should you grow tired of floating becalmed, here's your adrenal fix, and diving's best E-ticket ride. Colorado River currents below Hoover Dam and Lake Mead can whip along at 10 to 15 knots, and divers who hop into said currents can whip along with them. Try drift diving The Chute, about five miles from the base of the dam. Here the river narrows, and you make like Superman whipping past a sunken wooden tow barge and the occasional warp-speed trout. Exciting stuff. "We've had divers use up an entire tank of air in 10 minutes and come up with their eyes bulging," says local dive operator Drew Bodin.