Water has shaped the American West. Nowhere is this more evident than along the Front Range of Colorado. At the west end of the famous Great Plains rainfall gradient, the Front Range extends most of the length of Colorado and is one of the fastest growing metropolitan regions in the nation. Annual precipitation along the Front Range averages about 16 inches, and regional development has been possible only through the manipulation of Rocky Mountain rivers. Since the late 1830s, human changes to water flows have gone from the destruction of the beaver - the earliest water impounders and sediment trappers - to managing and moving just about every drop of available water. The distinctive river flow regime, with seasonal peak discharge driven by spring snowmelt, has been harnessed to accommodate agricultural, industrial, and municipal use, especially to the city of Denver and its ever-expanding metropolitan area. The Front Range of Colorado has no unappropriated water left, which means that any new use of water, including instream flow protection for aquatic and riparian habitat, will require either a reallocation from an existing use or importation of water from another basin.