This paper describes the salinity, temperature, dissolved oxygen and inorganic phosphate distributions for the Brazil northern coast, with special reference to the marine environment off the Amazon and Pará rivers. The change in direction of the coast with the consequent change in the axis of the Guiana Current together with the large amount of suspended matter contributed by river waters, create peculiar conditions on the continental shelf. These conditions are also influenced by the wind and rain system. Out from the continental shelf Tropical Atlantic oceanic conditions are prevalent. In contrast to the very low fertility of the Guiana Current the coastal waters, directly influenced by the rivers, show a supersatu ration of dissolved oxygen. The nutrients absorbed by suspended matter are partly liberated when the rivers mix with the oceanic water. However, the low light penetration restricts the oxygen production to only few meters.