It is surrounded by the more populated parts of Colombia and is threatened by farming, ranching, logging, oil exploitation and water pollution in the main rivers.

It includes the flat landscape along the lower course of the Magdalena River, and extends west over the coastal plain to the Gulf of Urabá.

In the center of the ecoregion the rivers form the ciénagas (wetlands), a large system of marshes, lakes and ponds, of great importance to resident and migratory birds.

[3] The ecoregion has a seasonal climate, with dry periods in January–March, when strong winds carry clouds from the Caribbean to the southern serranías, and in July–August.

In the drier areas the vegetation is dense, high rainforest with a rich understory, with great diversity of flora.

Large trees include Anacardium excelsum, Cariniana pyriformis, Caryocar amygdaliferum, Caryocar glabrum, Cedrela odorata, Ceiba pentandra, Cordia gerascanthus, Hymenaea courbaril, Myroxylon balsamum, Ochroma lagopus, Schizolobium parahyba and Tabebuia rosea.

There are more than 150 species of orchid, including Cattleya warscewiczii, Cycnoches chlorochilon, Peristeria elata and Psychopsis papilio.

[3] Large mammals found in the rain forests or wetlands include Geoffroy's spider monkey (Ateles geoffroyi), cotton-top tamarin (Saguinus oedipus), white-footed tamarin (Saguinus leucopus), jaguar (Panthera onca), cougar (Puma concolor), ocelot (Leopardus pardalis), jaguarundi (Puma yagouaroundi), crab-eating raccoon (Procyon cancrivorus), giant anteater (Myrmecophaga tridactyla), South American tapir (Tapirus terrestris colombianus), red brocket (Mazama americana), gray brocket (Mazama gouazoubira), capybara (Hydrochoerus hydrochaeris) and West Indian manatee (Trichechus manatus).

[3] Endangered mammals include black-headed spider monkey (Ateles fusciceps), Geoffroy's spider monkey (Ateles geoffroyi), red-crested tree-rat (Santamartamys rufodorsalis), white-footed tamarin (Saguinus leucopus) and cotton-top tamarin (Saguinus oedipus).

[3] Endangered birds include the recurve-billed bushbird (Clytoctantes alixii) and blue-billed curassow (Crax alberti).