The Guianan mangroves ecoregion extends along the Atlantic coasts of northeastern Venezuela, Guyana, Suriname, French Guiana, and Cabo Orange in Brazil.

Sand and shell ridges and elevated mud flats are formed by accumulated sediments, carried steadily westward from the mouth of the Amazon by strong ocean currents.

The Oronoco river has an average flow of 36,000 cubic metres (1,300,000 cu ft) per second, and deposits 200,000 tons of sediment each year, resulting in a very unstable landscape.

There are wide belts of Rhizophora in the inner estuary, with Avicennia on higher ground, sometimes mixed with Pterocarpus officinalis, Symphonia globulifera and Vitex species.

Dominant species include Costus arabicus, Cyperus giganteus, Eichhornia crassipes, Heliconia psittacorum, Roystonea regia and Mauritia flexuosa.

Muddy forests on ground that is almost always flooded have a single dense stratum of trees with heights from 15 to 25 metres (49 to 82 ft) such as Pterocarpus officinalis, Symphonia globulifera, Tabebuia aquatilis, açaí palm (Euterpe oleracea), Manicaria species and Mauritia flexuosa.

The mangrove belts hold Laguncularia racemosa on the seaward side, mixed with Spartina species of salt marsh grass, in front of stands of Avicennia germinans.

It is the largest area in South America where migrating shorebirds from the Nearctic realm spend the winter, with up to 5 million birds visiting in one year.

Bird species include scarlet ibis (Eudocimus ruber), black skimmer (Rynchops niger), gull-billed tern (Gelochelidon nilotica), short-billed dowitcher (Limnodromus griseus), lesser yellowlegs (Tringa flavipes), greater yellowlegs (Tringa melanoleuca), black-bellied whistling duck (Dendrocygna autumnalis) and tricolored heron (Egretta tricolor).

[1] More than 50 species of mammals have been recorded, including opossums, bats, tufted capuchin (Sapajus apella), common squirrel monkey (Saimiri sciureus), Venezuelan red howler (Alouatta seniculus), white-faced saki (Pithecia pithecia), giant anteater (Myrmecophaga tridactyla), jaguar (Panthera onca), cougar (Puma concolor), ocelot (Leopardus pardalis) and capybara (Hydrochoerus hydrochaeris).