Dancing in the Water   “You can’t swim without a lifeguard.” The voice cuts through the hum of the lake. I crane my head and find a blur of bodies gathered around a campfire further down the shore. Their faces melt together into a smear of orange and brown above the flames. A girl—teenager, maybe—stands at the edge of the group with two hands outstretched on either side of her mouth. From this distance, her face is round and nickel-sized, and her features are impossible to make out, but she...