Increasing water temperatures and frequencies and intensities of extreme weather events, (e.g., droughts and floods) associated with climate change have important consequences for stream organisms. I will present four examples of investigations done in collaboration with my students and colleagues at the Rocky Mountain Biological Laboratory of the negative effects of climate change on algae, insects and trout in high elevation streams of western Colorado, USA. First, increasing water temperatures accelerates development, increases mortality and decreases fecundity of Baetis mayflies. Second, recruitment of Baetis is threatened by early drying of oviposition sites during drough years. Third, the prevalence of a nematode parasite of Baetis is higher in years when snow melt and peak stream flows occur earlier, a trend observed over the past 40 years. Fourth, earlier seasonal snowmelt and peak flows also facilitate proliferation of the nuisance diatom (Didymosphenia geminata), which changes the composition of stream insects from predominance of mayflies to lower quality food species (midges) and thereby reduces growth rates of trout. Didymo blooms also create habitat favorable to oligochaetes, which are the intermediate host for a debilitating parasite of trout (whirling disease). These findings have implications for the consequences of managing flows leaving too little flow in trout streams. Such disruption of the natural flow regime via climate change and inappropriate management strategies could jeopardize the sustainability of otherwise pristine mountain streams.