A satellite view of Marajo
|Area||40,100 km2 (15,480 sq mi)|
|Length||297 km (184.5 mi)|
|Width||204 km (126.8 mi)|
|Highest elevation||40 m (130 ft)|
|Highest point||Breves (city)|
|Largest city||Breves (pop. 99,223)|
With a land area of 40,100 km² (15,500 sq mi), which compares in size to Switzerland, it is the largest island to be completely surrounded by fresh water 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 fresh water for some distance from shore. The city of Belém lies to the south across the southern fork (also called the Pará River) of the river's mouth. The island sits almost directly on the equator.
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.
The east side of the island is dominated by savanna vegetation. There are large fazendas with animal husbandry. This is also the location of Lake Arari, which has an area of 400 km² but shrinks by 80% during the dry season. There are large herds of domesticated water buffalo on the island. The west side of the island is characterized by Várzea forests and small farms. Lumber and açaí are produced there.
To the north of the large savanna area are palm swamps, mainly with Buriti Palm (Mauritia flexuosa) and Euterpe oleracea. During the rainy season, the swamps are flooded one meter high. Little is known about the ecology of these swamps.
There are 20 large rivers on the island.
Because of oscillating water levels and regular floods, many settlements are built on stilts (Palafitas).
The most important towns are in the southeast of the island: Soure, Salvaterra, and the largest city, Breves. They feature a basic touristic infrastructure and are popular because of the generous lonely beaches.
The island is shared by 16 municipalities of three microregions:
The island was the site of an advanced pre-Columbian society, the Marajoara culture. The island is also the location of the Roman Catholic Territorial Prelature of Marajó. In the 1918–1919 outbreak of the Spanish influenza, Marajó was the only major populated area in the world not to have documented any cases of the illness. 
- Development Plan for Marajó, Document of the Government of Brazil
- Ryan, Jeffrey, ed. Pandemic influenza: emergency planning and community preparedness. Boca Raton : CRC Press, 2009. p. 24
|Wikimedia Commons has media related to: Marajó|
- Marajó Island and Pará state www.v-brazil.com