The River That Runs Downhill

Water always seeks the lowest place. It never climbs upward on its own. From mountain snowmelt to valley stream to ocean floor, water pours itself out in one direction — down. And yet this downward journey is precisely what makes water the most life-giving substance on earth. The Nile's annual flooding enriched Egyptian farmland for millennia. The Columbia River carved channels that sustain salmon runs feeding entire ecosystems along the Pacific Northwest.…