Glacial watersheds can provide diverse foraging and growth opportunities to aquatic consumers through the juxtaposition of cold, meltwater mainstems with warmer, rain-fed tributaries and floodplain channels. Adjacent habitats often display stark contrasts in food availability, temperature, and other environmental parameters on small spatial scales. While streams fed by meltwater are classically considered unproductive, these harsh environments provide habitat for robust salmon populations in Alaskan watersheds. Meltwater streams may benefit fish by providing foraging opportunities when food availability in rain-driven streams is low, generating spatiotemporal asynchronies in growth potential. Our study investigates seasonal and interannual differences in juvenile salmonid growth between meltwater and rain-driven streams within a glacial watershed in Southeast Alaska. We collected cohort and individual growth histories of PIT-tagged juvenile Coho Salmon and Dolly Varden through intensive mark-recapture at three sites consisting of a glacial mainstem and two distinct rain-fed tributaries across two growing seasons, and generated growth curves that describe how growth rates change through time at each site. We also measured a diverse set of environmental parameters that characterize the distinct seasonal cycles of our meltwater and rain-driven streams. We found that the meltwater mainstem displayed significant differences in the seasonal timing and magnitude of fish growth when compared to rain-driven tributaries, creating asynchronies in growth potential between adjacent habitats. We also observed larger interannual variation in the magnitude and timing of peak growth within the meltwater mainstem when compared to the rain-driven tributaries. Spatial asynchrony and annual variation in growth were explained by differences in environmental conditions between streams. Our results suggest that the dynamic and variable conditions offered by adjacent meltwater and rain-driven streams provide a portfolio of growth opportunities that may support the resilience of fish populations. However, decreases in meltwater runoff is eroding environmental heterogeneity in watersheds undergoing rapid glacial melt, which is likely to temporally synchronize and simplify the growth landscape through the loss of unique growth trajectories associated with disappearing meltwater streams.