According to biologists, increasing streamflows is among the measures necessary to protect salmon and other native fish in the Pacific Northwest. Yet our understanding of the costs and most cost-effective approaches is hampered by lack of comparative experience. This article attempts to address both of these issues. The analysis finds that the costs of streamflow augmentation may be modest, between $1 and $10 per capita per year for the region. Apart from largE-scale actions on the Snake and Columbia Rivers, we find that streamflow augmentation will require decentralized approaches, and their cost-effective implementation will require localized scientific information, constant monitoring, and hands-on management to acquire water through purchases, leases, and contingent contracts when and where appropriate.