Somewhere in the deep green heart of central Florida, an eagle's cry pierces the morning quiet. Soaring through the sunrise, it surveys its domain before landing in a cypress tree high above the St. Johns River. As it fortifies its nest, an alligator bellows from the riverbank. Together, they play a primeval role in a story that predates memory.

Cruising the St. Johns River by houseboat, you step into that story and recapture a bit of what's lost in our workaday lives. After a few days, your body adapts to the rhythm of the tea-colored current and the stillness that marks the beginning and end of each day.

"Many people visualize theme parks when they think of Florida, but between Orlando and Daytona, it's a different world. There are places on this river that remind me of South America," said houseboating enthusiast Susan Bradley of St. Augustine, Fla.

Holly Bluff Marina in DeLand, Fla., offers houseboats for rent. Those who hop on one can travel this north-flowing river for several hours through forest and swamp before reaching Astor, a rustic fishing community in central Florida. With a quick wave to fishermen perched along the riverbank, travelers can leave Astor behind — and watch wilderness return.

Soon a new sight emerges: Lake George, Florida's second-largest lake. Continuing north, the river eventually picks up pace — and population — at Jacksonville, where it empties into the Atlantic.

There's no need to venture that far to discover the river's true beauty. Drop anchor off the main channel, and your boat is surrounded by a panorama of woods, wildlife and water reflecting an infinite expanse of sky.

Steve Moore, a live-aboard houseboat owner, wakes most mornings to see manatees or alligators swimming off the stern of his houseboat. He recalls the time a National Geographic photographer visited the St. Johns.

"He was amazed that this river looks so tropical," Moore recalled.

From Moore's perspective, the freshwater springs along the St. Johns are especially exotic. "They're unbelievably clear. It's like swimming through drinking water."

In summertime, the shimmering Blue Spring State Park, just south of the marina, fills with frolicking families. In cooler months, hundreds of slow-moving manatees graze in its 73-degree water.

Five hours north of the marina, boaters navigate Lake George by compass and channel marker (GPS is unreliable) to reach Silver Glen Springs. Raising the propellers and gliding carefully into the shallow spring run, boaters discover turquoise water glowing against the backdrop of Ocala National Forest. Swimming over the spring vents, snorkelers witness the force of nature that gushes forth 65 million gallons of water daily.

Except for holidays, the springs and other river anchorages promise a peaceful night.

"I've heard that silence is the new luxury, and I think that resonates with most people," Bradley said. "Our lives are so busy, being on a houseboat gives you the chance to move at your own pace."