The forests are seasonally flooded by whitewater rivers, which carry suspended sediment washed from the eastern slopes of the Andes and organic material.

The river course through the floodplain constantly shifts over time, creating oxbow lakes, levees, meander swales and bars.

These landscape elements support diverse vegetation adapted to flooding, which gradually merges into the surrounding terra firme forest.

[2] Economically valuable timber trees include Carapa guianensis, Iryanthera surinamensis, Ceiba pentandra and Calycophyllum spruceanum.

On the lower levees common trees include Pterocarpus santalinoides, Eschweilera albiflora, Piranhea trifoliata and Neoxythece elegans.

Other typical várzea trees are Parkia inundabilis, Septotheca tessmannii, Coumarouna micrantha, Ceiba burchellii, Ochroma lagopus and Manilkara inundata.

[2] There are two endemic primates in the Mamirauá Sustainable Development Reserve, the bald uakari (Cacajao calvus) and black squirrel monkey (Saimiri vanzolinii).

[2] Other mammals include white-lipped peccary (Tayassu pecari), common agouti (Dasyprocta genus), lowland paca (Cuniculus paca), jaguar (Panthera onca), capybara (Hydrochoerus hydrochaeris), spiny tree-rat (genus Echimys) and the Ega long-tongued bat (Scleronycteris ega).

Aquatic mammals include the Amazon river dolphin (Inia geoffrensis), tucuxi (Sotalia fluviatilis) and Amazonian manatee' (Trichechus inunguis).

[5] Large fruit-eating fish that enter the forest during the flood period include pacu (genera Metynnis and Mylossoma), tambaqui (Colossoma macropomum), pirarucu (Arapaima gigas) and sardinha (Triportheus angulatus).

Other fish include piranha (Serrasalmus species) and decorative fish from whitewater rivers and their blackwater tributaries and lakes such as blue discus (Symphysodon aequifasciatus), cichlids (genus Cichlasoma), characins (family Anostomidae), tetras (genera Hemigrammus and Hyphessobrycon), and catfish (families Aspredinidae, Callichthyidae, Doradidae and Loricariidae).

Smallholders along the rivers undertake mixed agriculture, forest exploitation, small-scale logging and livestock raising.