We are paddling offshore of Big Pine Key in the Lower Keys. Calm water reflects the azure sky, forming a Caribbean-like mirage. Beneath our hulls, a blue-green field of water frames darker shapes. The surface ripples like some giant's taut muscular skin. With each stroke, we fall into a living tapestry of sky and water.

In the virtual aquarium beneath our boats, we've seen a Southern stingray the size of a car hood on the silty bottom near the Barracuda Keys. Sharks schooled around us on the back side of Little Pine Key. In the Dusenbury Grottos, tiny starfish cling to sponges on red mangrove roots. A skinny fish tailed across the flats off Dreguez Key, its prey firmly lodged in vice-grip jaws. And minutes after this display of raw nature, a small seahorse, a most delicate creature, swam past.

Every day can be extraordinary in the Keys. From mangrove-lined creeks around Key Largo to Magnificent Frigatebirds soaring above the remote Dry Tortugas, these shallow tropical waters possess wonders-natural and man-made-unmatched in the continental United States.

UPPER KEYS

Drive over the Jewfish Creek Bridge near the end of the 18-mile Stretch, or over high-arching Card Sound Bridge, and you cross an imaginary line. Behind, mainland United States. Ahead, the Florida Keys, 100-plus miles of coral rock islands linked by a highway and 43 bridges, bounded by shallow waters of Florida Bay and America's only living coral barrier reef.

A quick stop at the Caribbean Club, setting for scenes from the 1948 movie Key Largo, sets the stage. Soaking in the atmosphere, listening to clattering wild parrots flock from one palm to the next, you spy out on Blackwater Sound a small boat moving slowly toward a far line of trees. It is a kayaker, headed out to explore Dusenbury Creek.

Within an hour of parking, you're slipping into a quiet creek. The canopy of red mangroves forms a winding tunnel. Sunlight dapples a leaf here, a spot of water there. Down into the clear water, fish swim away from your boat.

Mainland? What mainland? Welcome to the Keys.

If divers come to the Upper Keys for the offshore coral reef, kayakers come for clear, shallow nearshore waters. At Garden Cove, MM 106 on the oceanside, tips of turtle grass emerge from the water at low tide. Kayaks can skim across this watery meadow with ease to a creek entering Rattlesnake Key, a densely forested mangrove island. The canopy provides critical habitat for foraging and nesting birds.

Your approach may startle a heron or egret. ''Old Cranky'' is one nickname for these wading birds; their loud call -- an impatient-sounding ''gaaaak'' -- bears this out. Beyond Rattlesnake, five-mile-long Elradabob Key, inside John Pennekamp Coral Reef State Park, is riven with small mangrove creeks and tunnels to explore.

This kind of sheltered, nearshore paddling is characteristic of the Upper Keys. Near Tavernier, the narrow confines of Dove Creek empty into a quiet lake. And in the heart of busy Islamorada, it's possible to slip among the mangroves that line Little Basin to the small tuckaways where nurse sharks and rays lurk.

The dangerous business of salvaging ships that wrecked on the reef -- known as ''wrecking'' -- and an Indian massacre are two hallmarks in the history of Indian Key, a small lump of coral rock offshore of Islamorada that has figured prominently in Upper Keys history and lore. A one-time seat of Dade County, it is now a state park, as is nearby Lignumvitae Key, where there's evidence of an Indian burial ground.