A stream is an expression of its watershed; that is, liquid is literally “expressed” from an ecological matrix, the green breast of Earth, to form a ﬂow conﬁned by discernible banks. A stream’s water originates in snow, spring, and rain. At its head, it may ooze from a muddy slope; at its mouth, it spreads wide and gives itself to another body of water— a lake, a river, an ocean, or even another stream. Its velocities are various: it can ﬂow in ribbons, braids, or as ﬂat as a scarf. Sometimes a stream runs underground or deep in the Earth’s surface, as in Typee, where Herman Melville writes: “Starting to my feet, the sight of those dank rocks, oozing forth moisture at every crevice, and the dark stream shooting along its dismal channel, sent fresh chills through my shivering frame, and I felt as uncontrollable a desire to climb up towards the genial sunlight as I before had to descend the ravine.” A stream can also, eventually, cut through rock like a blade. A stream always moves under the spell of gravity. It is a medium for transport—silt, pollen, pine needles, and leaves ﬂoat its rapids and rifﬂes and are deposited in its bed. Under the water is that streambed, all rock-and-roll, a home for sediment and rock and a nesting ground for ﬁsh. Steelhead, trout, and salmon lay their eggs one to three feet deep in a gravel redd, while benthic invertebrates such as stoneﬂies, mayﬂies, blackﬂies, and caddis ﬂies hide in a stream’s cobbles. A stream is dynamic—and it receives, and thus reﬂects, the abuses that have taken place on the land.