The spatial variability of stream algae can be enormous, yet we lack an understanding of the biotic and abiotic factors that produce this unique characteristic of streams, particularly at large spatial scales. We tested the degree to which grazers control spatial heterogeneity of algae by removing insects from 50-100 m² areas of streams using electroshocking. We quantified changes in spatial structure of algal biomass before and after insect removal in three treatment and reference streams by using geostatistics. Whether consumers increase or decrease algal variability depends upon the variability caused by other factors, such as hydrology, substrate, and nutrients. We hypothesized that by selecting high algal biomass patches, grazers may decrease algal heterogeneity. Indeed, grazers caused a 3-fold reduction in algal spatial variability. Additionally, grazers caused a 4-fold decrease in the average patch size of algae, from 58 to 17 m. By removing grazers from a large area of a natural stream, we discovered that abiotically generated spatial structure of stream algae is heterogenous and that grazing insects reduce the spatial variability of algal resources. Studies that assume or construct initially homogenous distributions of resources may misrepresent the true effect of consumers on resource heterogeneity that occurs in natural streams.