After a sticky morning in May's soupy heat, the inland lagoon on the Florida Keys' Islamorada feels chilly at 70-some degrees. Six of us dip in cautiously, tugging on flippers, treading water and eagerly spreading out.

Once a quarry used to build bridges across the Keys, this three-acre saltwater lagoon is home to eight dolphins that are the heart of Theater of the Sea, a family-owned attraction since 1946. As the world's second-oldest marine animal park, it was also one of the first to offer swims with dolphins.

Early morning downpours have left the water cloudy, making it tricky to see Duffy and Stormy as our trainer pipes her whistle and they dive beneath the surface.

We wait with our arms cradled, excited and a little nervous, not knowing which of us the dolphins will choose first.

"Oh!" I gasp as Duffy — clocking close to 500 pounds — suddenly settles against me. He feels surprisingly soft rather than slippery. He's gentle, too, and radiates unexpected but welcome warmth in the cool water.

As we've been coached, I resist the urge to hug him close or stroke him above wise, mischievous eyes.

Duffy lingers briefly before swishing forward to the next person, each face lighting up in succession.

At least three sites offer swim-with-dolphin programs in the Lower Keys. Theater of the Sea claims the country's third-oldest program and more than 200,000 participants since 1987. The park gradually added more interactive programs that let guests work with sea lions, rays and sea turtles. Two of them let you paint a picture with dolphins or sea lions.

Before I signed up for my own dolphin swim, I tagged along to watch a morning encounter after meeting its participants on Theater of the Sea's pontoon ride across the lagoon. The group included a husband and wife from Connecticut and a trio of Bible study friends from Tennessee.

The wife, Catherine DeCosta, requested a life jacket and was clearly unsure about this wild encounter. Within minutes, though, she was treading water with confidence and enamored of her new finned friends. Her husband, Ed Pinder, let loose a deep rumbling laugh as one of the dolphins — cued to kiss him with a touch of a bottlenose — decided to linger, apparently tickled and intrigued by the texture of his beard.

"I still think kissing a girl is better," Pinder hollered, a grin plastered across his face.

Each group gets to choose four to five interactions, such as rubbing the dolphins' bellies, doing side-by-side upright spins, a slow swim alongside a dolphin or high-speed rides across the lagoon.

The dolphins' permanent smiles and playfulness infuse everyone with the irresistible joy you feel watching a dog gleefully snout-surfing out a car window. It's contagious, even if you're not in the water.

"This made the whole trip," Pinder said afterward.

"Best choice ever," readily agreed Cara Nash and her Nashville girlfriends. "We've all had swimming with dolphins on our bucket list."

Vintage park has its own vibe

The 17-acre Theater of the Sea feels tiny, old-school and charming compared with Orlando's highly polished Sea World and Discovery Cove, which sprawl across 230 acres.

Instead of lining up for a stadium show, Theater of the Sea visitors often begin with the dubious-sounding "bottomless" pontoon ride. Partway through the trip across the lagoon, Sherman the dolphin gracefully jumps up through the open middle of the pontoon and through a hoop just a few feet from passengers.

Florida's Keys don't have room for gargantuan theme parks, nor do they seem to fit the character and fierce independence of locals who rallied to secede from the United States as the Conch Republic in 1982.

Every place in the Keys seems to be within walking distance of the ocean and seamlessly knit to its many creatures. Family-run attractions take tourists fishing, snorkeling, diving and let you feed tarpon, which rocket out of the water to snap at bait dangled from a dock. Nonprofits do everything from using dolphins to work with mentally handicapped kids and adults to healing injured sea turtles at a midcentury hotel turned into turtle hospital.

Theater of the Sea feels fits right in with its laid-back pace and intimate feel. It's far more affordable than Orlando parks and easily doable in half a day, leaving time to dawdle or head back to the ocean.

I dropped behind my group and missed most of the parrot show ahead as I was drawn to the quiet snorkeling lagoon at the end of the mangrove walk. I waded into the water, utterly enchanted by electric blue and rainbow-hued parrotfish. They undulated toward me like a shimmering fan.

Spying a feed machine on shore, I scrounged for the best quarter I've ever spent.

The man at an empty beach bar nearby didn't bat an eye as I stood there laughing all by myself with fish bumping gently, then greedily into my legs, gulping pellets and eating from my hand. I gratefully found another quarter to repeat the Technicolor frenzy.

Making a splash

As the clock nudged toward 2:30 p.m., I could hardly wait for my own dolphin swim. Our group was to take turns cradling Stormy or Duffy and waiting for the bottlenose kiss.

Before long, the fun revved up, as we each grabbed a fin for a short, speedy ride across the lagoon. I waved elatedly, feeling like a modern Ethel Merman.

Then it was time for the final thrill: the foot push. I nervously locked my knees and ankles and waited to feel Stormy nose into the bottom of my foot.

Her 600 pounds of hydropower launched me explosively upward with a "Whoosh!" She is so strong that I was almost standing upright as we churned across the water; I was reveling in pure exhilaration.

I flashed back to watching Pinder's foot-push ride and understood why he threw out his arms and triumphantly shouted "Aquaman!"

After reluctantly saying goodbye to the dolphins, I strolled back to the Postcard Inn beach and stared at the glittery ocean with a fresh appreciation for what lies below its surface.

As I waded into the water, a voice in my head piped up "Aquawoman!" and a giddy grin lingered through sunset.

Minnesota travel writer Lisa Meyers McClintick wrote the guidebook "Day Trips From the Twin Cities" and the travel app Minnesota Lake Vacations.