Based on population data provided by the 2000 IBGE census, the volume of domestic sewage, the volume of treated sewage, the potential and remnant domestic sewage loads and the equivalent carbon and nitrogen loads were estimated for each one of the 645 counties of the São Paulo State and for the catchments of the rivers Piracicaba, Mogi-Guaçu, Turvo, Peixe, Aguapeí, São José dos Dourados, Itapetininga, Apiaí, Taquari, and Paranapanema. In order to estimate these parameters the existence of sewage collecting system, and the existence of any kind of sewage treatment in each county of the State were taken into account. The database generated in this study may be found at www.cena.usp.br/biota. Despite of the historical attempts of the São Paulo State government in treating sewage, only 17% of the sewage volume produced in the State has some type of treatment before it is launched to rivers. Consequently, the load of untreated sewage is indeed very large. This input of extra organic matter causes severe alterations in water bodies. Among the catchments we have analyzed the Piracicaba River basin is the most affected by domestic sewage, followed by Mogi-Guaçu and Turvo basins. On the other hand, the basins of the rivers Itapeteninga, Apiaí, Taquari and Paranapanema are the least affected.
rivers; watersheds; pollution; sewage; organic load