On summer weekends I swim in a nearby pond. Its water is as dark as Darjeeling tea, the hue owing to the pond’s bed of decayed leaves and organic matter cast off from the masses of trees and plants ringing its banks. The resulting sludge teems with microbes, insects, and all the other minute creatures that feed the snakes, snapping turtles, and bluegills I see as I do my lonely laps. Plants likewise feast on the nitrogen and phosphorus present, and as they grow, flower, and die, they themselves become part of the ooze. Its this virtuous cycle of rot and rebirth that makes ponds and other bodies of water throngingly alive.