Hydrology
The Nouabalé-Ndoki Park is named after two of its rivers. The Nouabalé (Mabale) River, within the north of the Park, flows east to the Motaba River. The northeastern border of the Park is delimited by the Lopia (Lofi), Mokala, and the Motaba Rivers, all of which drain eastwards. The edge of the marshes of the river Likouala aux Herbes, which flows southeastwards, form the southeastern border. Finally, the Ndoki itself is a wide, heavily vegetated river that forms the southwestern border of the Park. Thus, the Nouabalé-Ndoki National Park contains the headwaters of three of the four major river systems draining the North of the country (the fourth river is the Ibenga whose headwaters begin in the peripheral zone of the NNNP).
The southern part of the Park is particularly rich in wide river courses mostly rendered impassable by thick swamp vegetation. The Ndoki and Goualougo and their associated swamp forests to the south and west, and the swamps of the Likouala aux Herbes to the east have long been a barrier to human movement and have been instrumental in keeping the Nouabalé-Ndoki area relatively undisturbed.