A survey of the benthic macroalgae and physical data was monthly performed in Rio Savegre from its headwaters to its lowplain course. The macroalgae were observed with a viewing box at 20 cm intervals following a fixed rope across the stream and microscopical observations were made at laboratory. The species composition of benthic macroalgae found in Rio Savegre is characteristic for unpolluted. clear. carbonate poor streams. From the source to the mouth a change from species adapted to cold. fast flowing streams to species adjusted to higher temperatures. lower current velocity and periodic desiccation was observed. There was a replacement of the multilayered. well structured macroalgal community in the upper part of the river by surface films formed by microalgae in the lower part. In addition a high-light community consisting of Spirogyro sp., Nostoc verrucosum and Tetraspora sp. could be distinguished from the dim-light species Prosiola mexicana and Hildenbrandia sp.Durante un período de un año se estudió la composición de macroalgas en el Rio Savegre, Costa Rica a lo largo de un gradiente longitu­dinal desde el nacimiento del río (3200 m.s.n.m.) hasta su desembocadura (10 m.s.n.m). La composición de especies de macroalgas en el Rio Savegre corresponden a característica de agua no una comunidad contaminada y nos pobres de carbonato; así como especies adaptadas a bajas temperaturas en la parte superior del rio y especies adap­tadas a altas temperatures en la sección infe­rior del río. Las especies comunes en la parte superior del rio corresponden a Nostoc verrucosum, Te­traspora sp., Spirogyra sp. y Prasiola mexi­cana. En la pane baja del Rio Savegre domi­nan Gongrosiro sp.. Chamaesiphon pseu­dopolymorhus, Dichothrix orsiniana var. afri­cana, Hamoeothrix sp., Pleurocapsa sp., Pseudanabaena sp., Rivularia sp. y Sipho­nonema sp.