[2] The middle and upper regions of this river are separated by the Boa Esperança Hydroelectric Power Plant dam, but is otherwise navigable.

[3] The fish species richness in the Parnaíba River Basin has traditionally been considered impoverished, but this has been disproven by recent surveys, which have recorded about 140 native species (including several that remain undescribed) and about 40% of these are endemic.

[5] The river's delta has large stands of mangrove,[6] as well as dunes, beaches, marshes and other habitats.

[7] The delta is considered an Important Bird Area and is home to species such as scarlet ibis (Eudocimus ruber) and rufous crab hawk (Buteogallus aequinoctialis).

[7] Two species of aquatic turtles are endemic to the general region, the Maranhão slider (Trachemys adiutrix) that is found in the delta and the side-necked turtles Mesoclemmys perplexa found inland, but neither is entirely restricted to the Parnaíba River Basin.