The ecoregion is bounded by the Maranhão mangroves and the Northeastern Brazil restingas along the coast to the north, the Tocantins–Araguaia–Maranhão moist forests of Amazonia across the Pindaré River to the northwest and west, the Cerrado tropical savanna to the south, and the Caatingas xeric shrublands to the east.

The dominant tree in the region is the Babaçu palm (Attalea speciosa), an oil palm that occurs naturally along the southern edge of the Amazonian forests, but whose predominance has been extended by its tolerance to human-caused fires and forest clearing.

Herons and other aquatic birds are usually seen along the rivers banks and lake margins while hunting for crustaceans and fish.

The amphibians are also abundant, being more common during the raining season, when it is possible to see a great number of toad and frog species.

In the water there are many species of animals such as fishes that belong to the Cichlidae and Characidae families and many crustaceans as well, some of these are freshwater shrimps and crabs.