an environmental assessment about phosphorus and nitrogen species was carried out in waters of São Francisco Falso River, tributary of Itaipu Reservoir. Results from four field campaigns showed that trophic state vary of oligotrophic to mesotrophic, being the latter observed under rain influence. Among nitrogen species, NO2 presented concentration above guide-value recommended by Canadian environmental agency, what means a risk for aquatic life. In comparison to Ocoí River, another tributary of Itaipu Reservoir, São Francisco's waters showed better quality.
eutrophication; hydrographic basin; trophic state index
