Background: Several studies of lotic ecosystems have provided important ecological information on the influence of environmental heterogeneity on macroscopic algae composition. Hypothesis:The highest species diversity will occur during the cold-dry season, correlated to low temperature and oligothrophic water, while the distribution of each species will be related to heterogeneity of habitat and its dispersal strategies.Studied species: Twenty-two species of macroscopic algae of different Phyla (Chlorophyta, Cyanobacteria, Heterokontophyta and Rhodophyta). Study site:The macroscopic algae composition was described for 35 permanent mountain streams in the Basin of Mexico from 2012 to 2015.Methods: Algae species, physico-chemical water conditions and microhabitat factors were recorded in situ at each contrasting season. The relationship between diversity and the environmental factors was statistically evaluated by Canonical Correspondence Analysis and a Spearman test. Results:Macroscopic algae recorded had biological features and environmental abilities that separated them into two groups. The first included the most frequent and abundant species: Nostoc parmelioides, Placoma regularis, Prasiola mexicana and Vaucheria bursata. The second included species restricted to certain habitats: Draparnaldia mutabilis, Tetraspora gelatinosa, Batrachospermum gelatinosum and Paralemanea mexicana. Each Phyla responds differentially to the spatial heterogeneity of the streams, but the species does not change between contrasting seasons. Conclusions:Local and spatial environmental variables explain differences in richness and distribution of species on the studied area; however, species composition does not vary widely among sampling sites. Cyanobacteria and Chlorophyta are more affected by local environmental variables, whereas Rhodophyta is more influenced by spatial variables.Keywords: Aquatic communities, Basin of Mexico, macroscopic algae, mountain streams. ResumenAntecedentes: Diversos estudios de ecosistemas lóticos han aportado información ecológica importante sobre la influencia de la heterogeneidad ambiental en la composición de algas macroscópicas.Hipótesis: La mayor diversidad se presentará durante la estación fría y estará relacionada con la baja temperatura y las condiciones oligotróficas del agua; mientras que la distribución de cada especie estará relacionada con la heterogeneidad del hábitat y las diversas estrategias de dispersión.Especie en estudio: Veintidós especies de algas macroscópicas de diferentes Phyla (Chlorophyta, Cyanobacteria, Heterokontophyta y Rhodophyta). Sitio de estudio:Fue estudiada la composición de algas macroscópicas en 35 ríos de montaña de la cuenca de México, entre 2012 y 2015.Métodos: Las especies, las variables fisicoquímicas del agua y microambientales fueron registradas in situ durante las estaciones más contrastantes. La relación entre la diversidad y los factores ambientales fueron evaluados estadística-mente a través de un Análisis de Correspondencia Canónica y una prueba...