The potential role of predatory fish and grazer type in determining patterns of benthic algal assemblages in high-altitude streams was investigated in western Colorado. A two-factor experiment was conducted in 12 naturally fishless first order spring-fed streams, with fish cues (present vs. absent) and dominant grazer type (scrappers-caddisflies- vs. browsers –mayflies-) at starting conditions as factors. We introduced fish cues in 6 randomly selected streams (3 for each grazer type stream) by including two Brook Trout in 110L plastic bins for 4 weeks. Fish cues did not affect the abundance or physiognomy of epilithic assemblages. However, differences in the physiognomy of algal assemblages among the streams were attributed to the interaction between fish and grazer type stream. While fish cues did not affect grazer abundance or algal composition in streams initially dominated by caddisflies, fish cues increased both the abundance of grazers and postrate diatoms in the mayfly streams. We hypothesize that caddisfly grazers are less vulnerable to fish predation, and therefore, their effects on the algal community should be unaltered by fish cues. In contrast, mayfly grazers are more vulnerable to predation, and fish cues should have greater impact on grazer behavior, with cascading effects on algae physiognomy.