The Monkey River is one of six large watersheds in the 1 million acre (4,000 km2) Maya Mountain Marine Area Transect, which connects the Maya Mountains to the coastal waters of the Gulf of Honduras.
The Monkey River drains much of southern Belize through the Bladen (southern) Branch, which includes tributaries from a part of southern Guatemala and the southern slopes of the Maya Mountains in Belize, containing the ancient Mayan sites of Nim Li Punit and Lubaantun.