Situated in the Mosquita region of north-east Honduras, the site comprises a belt of approximately 15 km by 150 km which extends inland from Laguna de Ibans and Laguna de Brus on the Caribbean coast in a south-westerly direction. The coastal towns of Palacios and Brus Laguna lie approximately 5 km from the park boundaries on either side of the reserve.
The reserve protects virtually the entire watershed of the 100 km long Plátano River, as well as major portions of the Paulaya, Guampu and Sicre rivers. These three waterways and the Caribbean form the boundaries of the reserve. Topographic relief falls into two broad categories: the rugged mountainous headwaters region which encompasses almost 75% of the reserve, flanked by the Plátano River and rising to Punta Piedra, and the coastal plains. The mountainous area has remarkable rock formations (e.g. Dama Peak) and a waterfall of 500 m. The coastal area is flat or undulating with a number of lagoons such as Ibans and Cartina and grasslands subject to winter flooding. The river basin drains an area of some 130,000 ha and meanders considerably in the lowland region, marooning several oxbow lakes. Natural levees have built up along much of this stretch and are preferred terrain for small agricultural plots. The upper two-thirds of the river course are through mountainous terrain. Part of the river is subterranean below huge basalt rocks.
This is the largest surviving area of virgin tropical rainforest in Honduras and topographical diversity has resulted in a wild array of ecosystem types. The two dominant life zones are Humid Tropical Forest and Very Humid Subtropical Forest. The majority of the reserve (about 85%) lies within the tropical moist-forest zone, and 10-15% in the subtropical wet-forest zone. Mangrove ecosystems fringe the coastal lagoons of Brus (brackish) and Ibans (freshwater). Inland from the beach is a broad coastal savannah which consists of sedge prairie in the wetter areas, grasses in drier areas, and pine savannahs. Hardwood gallery forest occurs along the Plátano River and other alluvial tributaries. On land disturbed by agriculture dominates the secondary forest. The greatest portion of the watershed is blanketed by mature broadleaf forest. Important timber trees occur within the reserve. Pines and several palm species are used locally for construction, and some timber species are made into dugout canoes.
39 species of mammal, 377 species of bird and 126 reptiles and amphibians have been recorded. Threatened species include giant anteater, Baird's (Central American) tapir, jaguar, ocelot, puma, margay, jaguarondi, Central American otter, Caribbean manatee, American crocodile, brown caiman, red brocket deer, harpy eagle, scarlet macaw, green macaw, military macaw, king vulture, great curassow and crested guan. Reptiles include green turtle, loggerhead turtle and leatherback turtle.
The site of Ciudad Blanca (White City) within the protected area constitutes one of the most important archaeological sites of Mayan civilization. Archaeological remains include the Piedras Pintadas petroglyphs on the bed of the Plátano River, believed to belong to an unknown pre-Columbian culture. The reserve also contains the site where Christopher Colombus first landed in the Americas in 1492. There are some 200 sites of archaeological importance.