In an effort to understand these conditions and to improve them for the enhancement of fish populations, the USBR commissioned two models that were to provide insight to flows in the Klamath River and their effects on fish habitat: a reconstruction of what “natural” flows might have been like without dams in place (the Natural Flow Study), and a model to predict the distribution of fish habitats (the Instream Flow Study). These models operate within the general physical matrix described in this chapter, and they deal with the fish populations defined here. The remainder of this report explores the products of these research models.