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/ Water temperature is almost certainly a limiting factor in the maintenance of a self-sustaining rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) and brown trout (Salmo trutta) fishery in the lower reaches of the Cache la Poudre River near Fort Collins, Colorado, USA. Irrigation diversions dewater portions of the river, but cold reservoir releases moderate water temperatures during some periods. The US Fish and Wildlife Service's Stream Network Temperature Model (SNTEMP) was applied to a 31-km segment of the river using readily available stream geometry and hydrological and meteorological data. The calibrated model produced satisfactory water temperature predictions (R 2 = 0.88, P < 0.001, N = 49) for a 62-day summer period. It was used to evaluate a variety of flow and nonfiow alternatives to keep water temperatures below 23,3~ for the trout. Supplemental flows or reduced diversions of 3 m3/sec would be needed to maintain suitable summer temperatures throughout most of the study area. Such flows would be especially beneficial during weekends when current irrigation patterns reduce flows. The model indicated that increasing the riparian shade would result in little improvement in water temperatures but that decreasing the stream width would result in significant temperature reductions. Introduction of a more thermally tolerant redband trout (Oncorhynchus sp.), or smallmouth bass (Micropterus dolomieul) might prove beneficial to the fishery. Construction of deep pools for thermal refugia might also be helpful.The Poudre River Trust, in cooperation with Trout Unlimited and the City of Fort Collins, Colorado, USA, has been working on a plan for the establishment and maintenance of a sport fishery in the Cache la Poudre River at Fort Collins (Pitts 1988). The plan is multifaceted, one element being the analysis of fishery potential and hydrology. A related, but separate, planning effort involves the study of this river corridor for possible federal designation as a National Recreation Area (Leaf, no date). These planning efforts give attention to recreation, water quality, floodplain development, and flood control.Both streamflow and water temperature are thought to be limiting factors in establishing a self-sustaining sport fishery in the lower reaches of the Cache la Poudre River. The flows in this river, especially near Fort Collins, are extensively manipulated during both summer and winter, primarily to support irrigated agriculture. Opportunities for flow manipulation by controlling agricultural depletions are extremely limited due to existing senior water rights. A proposed water storage reservoir above Fort Collins, however, offers an opportunity for flow enhancement through the city.The quantity and timing of streamflow necessary to support a coldwater fishery is being addressed through

Elevated water temperatures have been implicated as a factor limiting the recovery of anadromous salmonids in the Klamath River basin. This article reviews evidence of a multidecade trend of increasing temperatures in the lower main‐stem Klamath River above the ocean and, based on model simulations, finds a high probability that water temperature has been increasing by approximately 0.5°C/decade (95% confidence interval (CI) = 0.42–0.60°C/decade) since the early 1960s. The season of high temperatures that are potentially stressful to salmonids has lengthened by about 1 month over the period studied, and the average length of main‐stem river with cool summer temperatures has declined by about 8.2 km/decade. Water temperature trends seem unrelated to any change in main‐stem water availability but are consistent with measured basinwide air temperature increases. Main‐stem warming may be related to the cyclic Pacific Decadal Oscillation, but if this trend continues it might jeopardize the recovery of anadromous salmonids in the Klamath River basin.

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