Aim: We evaluated different dimensions of beta diversity (taxonomic, phylogenetic, and functional), and its components (spatial turnover and nestedness), of a stream macroalgal metacommunity, as well as the effect of local environmental variables, types of biome, and spatial factors on these dimensions and components. Location: Ten natural areas of southern Brazil, covering the main biomes represented in the region. Methods: We analyzed a data set collected in 105 stream segments using a dissimilarity partitioning approach to decompose total beta diversity (beta.SOR – multisite dissimilarity; beta.sor – pairwise dissimilarity) into spatial turnover (beta.SIM; beta.sim) and nestedness (beta.SNE; beta.sne) components. Furthermore, we assessed the effects of local environmental variables, types of biome, and spatial factors on beta diversity components by performing distance-based redundancy analysis (db-RDA), and its partial version (db-pRDA). Taxonomic data were tabulated considering four different species incidence matrices: total macroalgae; only green algae; only red algae; and only cyanobacteria. Results: For taxonomic and phylogenetic dimensions, very high values of total beta diversity (beta.SOR) were found for all species incidence matrices, with beta.SOR and spatial turnover (beta.SIM) showing strong correspondence to each other; nestedness (beta.SNE) had extremely low values. For the functional dimension, high beta.SOR value and a predominance of beta.SIM over beta.SNE were also found, but the difference between beta.SIM and beta.SNE was substantially lower than that observed for taxonomic and phylogenetic dimensions. In regard to taxonomic and phylogenetic dimensions, total beta diversity and spatial turnover were, in general, significantly related to local environmental variables, types of biome, and spatial factors for total macroalgae and green algae, whereas they were significantly related to types of biome and space for red algae, and only to local environment for cyanobacteria. Main conclusions: Our results showed, therefore, that spatial turnover was the main component of beta diversity regardless of the dimension and macroalgal species incidence matrix and that the relative influence of local environmental variables, types of biome, and spatial factors on the total beta diversity and its spatial turnover component can vary according to the dimension considered and by algal group.