 The river, once the primary source of fresh water in the city, is now one of its most polluted.Untreated sewage is the primary source of pollution of the Carioca; the stretch of the river in Guararapes and Cosme Velho are a great sources of unregulated sewage.The water of the Carioca carries pollutants that cause diarrhea, hepatitis, and leptospirosis.