We hugged its rocky coastline, waiting for it to soften into sand. Pumping our legs, gasping for air, scaling bridges. We wore our bathing suits under our clothes so that we could strip and swim. One afternoon, we ate soggy KFC biscuits in the rain on a wealthy, empty private beach just off the Rickenbacker Causeway, skipping the tollbooths and pushing our bikes through the sea grapes, our leg muscles still spasming from climbing the steep bridge that connects mainland Miami to the island of Key Biscayne. This was our longest ride; we had traveled, at most, 11 miles from our homes. I’m not sure why buying fried chicken with our parents’ money and eating it on the damp sand felt like the epitome of freedom, but it did.

Manatees in Dinner Key Marina. “Beware of Alligators” signs at Matheson Hammock. The stink of low tide, the tiny crabs waving their pitchfork arms at us from the exposed rocks like a mob of irate villagers. Somewhere, deep in the back of our brains, we could hear our parents yelling: ‘‘Slow down! Slow down!’’ Instead we let our arms extend into a fixed-wing soar over the handlebars, echoing the hundred gulls wheeling above us. Sometimes our parents’ flickery omniscience detected a breach in the system, and they’d notice, for example, that we’d returned home penniless with soaking hair. But ‘‘riding bikes’’ sounds so innocent, and we still had the round eyes of children. We had the bodies of women, which meant that men had begun to holler at us from passing cars, words that drew butcher-shop lines around us and made us consider ourselves as an assemblage of parts: breasts, asses, thighs, faces. During rush-hour traffic, we had to pedal through this uglier sort of thundershower, our faces burning. At certain intersections we knew to sit and hunch over the handlebars, our eyes on the pavement.

But once we made it over the bridge, the huge, blue solvent of the bay erased whatever hideous self-consciousness we’d felt while riding along the highway. To get to the beach, we had to stand to pedal, and then the fire left our faces and came from inside us, from our lungs and calves — I discovered how strong my body was on those rides, pushing uphill. We went shrieking downhill toward the wavy tarpaulin of the bay. At last, we could relax into the sea, with its beautiful elasticity, its deep and generous amnesia. Like us, Biscayne Bay could forget a violent storm in an instant. We swam through smooth water, hidden up to our necks, buoyed inside the happy silence that follows great physical exertion.

Under that moody, aqueous sky, my two best friends and I turned 14. I didn’t know then that I was coasting through the best summer of my life. In my memory, that summer is a suspension bridge over the water, connecting the worlds of childhood and adulthood. Fall came, and we started high school, a violent eviction from the freedom of those afternoons.

There are plenty of places that you can get to by bicycle, even in a city as vast as Miami. The gas-station convenience store that sells to minors. Tattoo parlors with a financial stake in believing that you are 18. The houses of male strangers willing to extend to you this same line of credit. The Planned Parenthood. When I think about the dark straits that young women have to travel, I remember racing the waves on either side of a winnowing road. The Biscayne Bay I’ve written about here is not a place to which I can return; in the past decade, some 25,000 acres of its sea-grass meadows — more than 90 percent in one part of the bay — have died, and its famous aquamarine color belies the devastation of raw sewage, chemical runoff, global warming and acidification, toxic blooms of algae. We three were not amnesiacs, as it turns out, and neither is the ocean; the damage we sustain lives on inside us. So does this memory: the bridge to a blue expanse of dreaming time that girls deserve, and not only for a summer.