Marajó Bay, the Marajoara Gulf or the Amazon Gulf, is a recessed body of water of the Brazilian coast located in the state of Pará. It is roughly 4,500 km (1,700 sq mi) in size, and is a receptacle for the waters of the Pará River distributary channel, the waters of the Tocantins basin and the waters of the Guajará Bay, serving as the eastern aquatic border of both the Marajó Island and the Marajó Archipelago. Marajó Bay is an estuary consisting of both salt and fresh water, resulting in the classification of an estuarine system. Marajó Bay also receives sediments from the Amazon River through the Breves Channel as well as the Pará River, causing the water to be turbid.
The Pará River and a small fraction of the Tocantins River are the main providers of water for Marajó Bay. The river is vital to the surrounding areas and makes different areas and ports very accessible for locals. The river also eventually clashes with salt water from the Atlantic Ocean in the Marajó Bay. A circulation process of salinity, temperature, and tidal range in the two different water types occurs in the bay as they meet. Salt water concentrations are also impacted by low water periods of the Amazon River.
