The evaluation of the degree of contamination of an aquatic environment is obtained by a correlation of data obtained experimentally. The data interpretation, besides the classification of local environmental conditions, is to find a predictable parameter behavior, indicating probable consequences of pollution damage. This understanding allows you to map the main sources of contamination, interrelating the data obtained with political, geographical and social conditions. A set of chemical (sterols, delta to the power of 13 C) and biological (thermotolerant coliforms) indicators were determined in particulate organic matter in order to investigate the natural contributions and domestic sewage contribution in representative rivers of the catchment region of Guanabara Bay (CRGB). Eight rivers in the CRBG were evaluated, three in the eastern sector (Caceribu , Guapimirim and Surui) and five in the western sector (Iguaçu , Meriti , Irajá, Cunha Channel and Mangue Channel). Samples were collected in three campaigns (Sep/2014, Jan/2015 and April/2015). The results of thermotolerant coliforms ranged between 400 and 1,1x10 to the power of 12 NMP/100ml, with a predominance, in all campaigns, of higher values in rivers of the west sector of the CRGB. The concentration of coprostanol showed similar variation as that of the coliforms, averaging 21,9 plus/minus 43,4 Microgram L to the power of minus 1 with a maximum value of 205 Microgram L to the power of minus 1 in the Mangue Channel. Diagnostic indexes based on selected sterols confirmed the general scenario of fecal contamination in the western sector of the CRGB. . The lowest values of both markers prevailed in the rivers of eastern Guanabara bay, particularly in the Environmental Protection Area of Guapimirim crossing rivers Caceribu and Guapimirim. Based on data from the literature of characterization of the organic matter from raw sewage (RS) samples, the percentage were calculated, for each study sample, that corresponds to RS. That is the fraction of river water equivalent to the untreated sewage. Thus, from the flow of the rivers were estimated sewage loads exported to the Bay. The results were worrisome. The lowest calculated load exceeded 2 tons of raw sewage exported every month, as referring to Caceribu river. In contrast, the São João de Meriti river indicated a monthly dump of more than 140 tonnes. Adding the eight rivers of the study, was stipulated monthly, the release of more than 400 tons of raw sewage in Guanabara Bay. It was also possible to identify the contribution of organic matter of continental origin in rivers with low fecal contamination. It was estimated that coprostanol levels between 0,060 Microgram L to the power of minus 1 and 0,240 g L tothe power of minus 1 correspond to the coliforms limited by CONAMA 274/2000 for primary contact. Therefore, the coprostanol may prove to be an additional indicator for assessing fecal contamination for the purpose of bathing in the bay waters. The river flow coming from the Mangue Channel, Cunha Channel and Meriti River are the largest contributors to the sewage supply to the Guanabara Bay. That situation is a direct reflection of population density and poor sanitation in the basins of these rivers.