[1] Almost all of the ecoregion is in the central northern part of the Brazilian Amazon basin, with a small portion in Colombia.

Conservation units include the Jaú National Park and the Mamirauá Sustainable Development Reserve.

[2] The lowland plateau that holds the Japurá–Solimoes–Negro moist forests ecoregion emerged as soft sediments about 2.5 million years ago.

The terrain is mainly non-flooded terra firme on wide plains cut by steep-sided valleys of tributaries of the larger rivers.

The blackwater Rio Negro and rivers of the interior of the ecoregion flood Igapó forests, with lower diversity of tree species and less fertile soil.

Other terra firme trees include Brazil nut (Bertholletia excelsa), sucupira (Bowdichia virgilioides) and rubber (Hevea spruceana).

[2] Trees in igapó forests along the Jaú River in the west include Elvasia calophylla, Swartzia laevicarpa, Pouteria elegans, Aldina latifolia, Swartzia polyphylla, Ouratea hexasperma, Mollia speciosa, Leopoldiana pulchra, Inga puntata and Heterostemon mimosoides.

Trees along the Tarumã Mirim River to the east include Vismia amazonica, Unonopsis guatterioides, Pentaclethra macroloba, Macrolobium suaveolens, Eschweilera parvifolia, Caraipa grandiflora, Aspidosperma nitidum and Mabea nitida.

[2] Timber trees on the upper margins of the várzea include Ceiba pentandra, Manilkara amazonica, and Virola surinamensis.

The forest is largely undisturbed and relatively stable, but there are high levels of mining, logging, agriculture, hunting and fishing along the rivers.

In the border region between Colombia and Brazil large stretches of river bank are being destroyed by gold miners.