Fish need water every day. For fish to have that water, rivers and streams must flow. Yet in the mid-19th Century, as miners and trappers moved west into a region where average rainfall was less than half of that in the East, few worried about the limits of the region's water supply. They adopted a water management system, the hallmark of which was the prior appropriation doctrine of "first in time; first in right." The earliest or most senior person to divert water to "beneficial use" - which at the time meant mining, irrigation or domestic use - had the most valuable water right. A senior user's right would be completely satisfied before a junior water user could take a single drop. The US government encouraged settlement by offering land for free to those who would farm it . Because average rainfall was not enough to grow crops, these settlers dug irrigation ditches to get water to their lands. During the mid-20th century, the federal government expended vast resources building ever larger and more complex dam and diversion systems that moved water long distances and stored vast quantities for use mostly by irrigators. By the latter half of the 20th century, many western rivers were "over-appropriated," meaning that every drop of water was spoken for - often several times over. Yet cities grew, slowly at first and then rapidly as people flocked to the West and made the region the fastest growing area of the country in the 1990s. All of this activity - and the diversions of water that accompanied it - led to declining fisheries and rivers drying up. It became apparent that the western states' peculiar system of water allocation was itself a roadblock to protecting or restoring flowing rivers for healthy fisheries and other instream benefits. States had not recognized leaving water in rivers as a beneficial use until the 1970s or later - long after many rivers' water was already fully allocated. While states adopted limited instream flow protection programs starting in the 1970s, these programs were just that - limited. Although some states (Oregon, Montana and California) established minimum base flows for some rivers, no state allowed individuals to hold instream flow water rights; only state agencies had that authority.
