Marajó Archipelago in Amazon River Mouth, Brazil0.9S 49.5W
Several islands can be observed in the delta lowlands at the mouth of the Amazon in the state of Pará, Brazil. The islands form part of the low-lying marajó várzea, the inundated land in and around the mouth of the Amazon River.
The islands offer an excellent place to observe the tidal bore called the pororoca, where the Amazon river waters meet the incoming Atlantic tides and form a standing wave.
The largest of these islands is Marajó, with a land area of 40,100 km² (15,500 sq mi), which compares to the size of Switzerland. It is the largest island to be completely surrounded by freshwater in the world. Although its northeast coastline faces the Atlantic Ocean, the outflow from the Amazon is so great that the sea at the mouth is quite unbriny for some distance from shore.
Together with smaller neighboring islands, separated from Marajó by rivers, it forms the Marajó Archipelago, with an aggregate area of 49,602 km² (19,151 sq mi). Large parts of the islands are flooded during the rain season, because of higher water levels of the Amazon River along the coast and of heavy rainfall in the interior.