The Paraíba do Sul (), or simply termed Paraíba, is a river in southeast Brazil. It flows west to northeast from its farthest source at the source of the river Paraitinga to the sea near Campos dos Goytacazes. The river receives its name when it meets the river Paraibuna at the Paraibuna dam. Its main tributaries are the rivers Jaguari, Buquira, Paraibuna, Preto, Pomba and Muriaé. These last two are the longest and join the main river and from the mouth respectively . The valley of the Paraíba do Sul ranges from the latitudes 20°26' and 23°39'S and the longitudes of 41° and 46°30'W and covers an area of about distributed over three states. The main economic activities are industry and cattle raising. Navigation Presently only two parts of the river can be navigated: The lower section, between the mouth and São Fidélis, about 90 km. It has a declivity of 22 cm/km. There is incipient navigation carried out by small boats that transport mainly construction material to the city of Campos dos Goytacazes. The upper middle section, between Cachoeira Paulista and Guararema, about . Despite the small declivity of 19 cm/km, navigation is restricted to tourist boats. Elsewhere navigation is hampered by various obstacles; waterfalls, rapids, sections with great declivity and various hydroelectric works with no locks. Other factors impeding navigation are the existence of highway and railway bridges, the proximity of roads and railways following the riverbank and the location of several cities on its banks. Centres of population The Paraíba Valley is very fertile and has always been a region of relatively dense population. Cities located on or near the river are State of Rio de Janeiro: Barra do Piraí Barra Mansa Três Rios Paraiba do Sul Sapucaia Campos dos Goytacazes - center of a rich sugar cane growing area Vassouras - site of a highly respected agricultural university Volta Redonda - site of Brazil's first steel industry) State of São Paulo: Aparecida - site of Brazil's most famous Marian pilgrimage site Guaratinguetá São José dos Campos - high-tech industry and home to Embraer, Brazil's aircraft manufacturer Taubaté - Volkswagen and Ford plants State of Minas Gerais: Além Paraíba Estrela Dalva Juiz de Fora - Important manufacturing city on the Paraibuna River, one of the major tributaries of the Paraíba. Ecology Unlike rivers in northern Brazil where seasonal variations in water temperature generally are relatively limited, those