According to organs of the Brazilian government there are 12 major hydrographic regions in Brazil. Seven of these are river basins named after their main rivers; the other five are groupings of various river basins in areas which have no dominant river.

     Hydrographic Regions named after their dominant rivers:
-Amazonas
-Paraguai
-Paraná
-Parnaíba
-São Francisco
-Tocantins
-Uruguai

    coastal Hydrographic Regions based on regional groupings of minor river basins (listed from north to south):
-Atlântico Nordeste Ocidental (Western North-east Atlantic)
-Atlântico Nordeste Oriental (Eastern North-east Atlantic)
-Atlântico Leste (Eastern Atlantic)
-Atlântico Sudeste (South-east Atlantic)
-Atlântico Sul (South Atlantic)
The Amazon River is the widest and second longest river (behind the Nile) in the world. This huge river drains the greater part of the world's rainforests. Another major river, the Paraná, has its source in Brazil. It forms the border of Paraguay and Argentina, then winds its way through Argentina and into the Atlantic Ocean, along the southern coast of Uruguay. The HBV hydrology transport model has been used to analyze certain pollutant transport in Brazil's river systems. The Amazon is full of eroded soil.