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Recommendations The magnitude of spring runoff flows in the Yampa River are relatively natural, with average flows reduced only about 5% to 6%. In contrast, baseflows have been reduced from historical flows by an average of 30% and up to 80% in dry years. As flows recede below a certain threshold, characteristics such as depth, wetted width, velocity, cross sectional area, etc., rapidly decline, creating loss of habitat stability, quality and quantity. The flow management recommendations in this report were determined by identifying curves breaks in geomorphic and hydraulic variables that form habitat for endangered fishes. Curve break flows represented the condition of maximum change in selected variables with reduced flow, and thus the greatest impact on the environment of endangered fishes. The lack of significant differences in curve break flows among variables and strata suggested a consistent response in the river channel as a function of flow. Estimates of the maximum rate change among river channel variables with low flows were comparable with, and supported by, estimates of weighted useable area for both Colorado pikeminnow and humpback chub, and risk estimates of potential barriers to migrational and local movement of fishes. Curve break analysis of channel variables suggested that baseflow management for endangered fishes in the Yampa River below Craig, Colorado should target 93 cfs. This baseflow management recommendation is slightly lower than curve breaks based on simulated (RHABSIM) habitat availability for endangered fishes and the flow defined as needed to prevent barriers to local movement. Instream migrational barriers do not appear to be problematic for returning postspawned Colorado pikeminnow. However, it is evident from the historic record that flows less than 93 cfs have been recorded at the Maybell gage. In 31 of 84 years of record less than 93 cfs have been recorded at the Maybell gage. During the same 84 years of record, flows of less than 93 cfs for a period in excess of 14 days or more have occurred in 19 years. Because flows have dropped below 93 cfs during the period of record at the Maybell gage, and endangered fishes are extant in the Yampa River, it appears that 93 cfs in not a threshold flow and will not reduce endangered fish populations ifviolated within the realm of historical frequency. Therefore we conclude that flows below 93 cfs is near the threshold flow that may be limiting to productivity of aquatic invertebrates and other aquatic organisms dependent on viability of riffle habitats. For long term recovery and stability of endangered fish populations, it is reasonable to maintain those organisms in the system that are dependent upon riffle production. 13