The Bas Ogooué is a large alluvial plain approximately 200 kilometres long and 70 kilometres wide, located in western Gabon. It includes marshes, lakes and river systems centred on the Ogooué River, and provides key hydrological functions such as flood regulation, water filtration, and shoreline stabilization. About half of the Site is covered by dense forest, riparian marshes and savannah. The wetlands support several threatened animals, including gorilla, chimpanzee, mandrill, elephant, hippopotamus, buffalo and African manatee. Notable birds include herons, African cormorants, and falcons. The fish community includes tilapia and carp species. The Site has cultural significance, being associated with traditional practices such as the Bwiti rite and the Okukwè mask tradition. It is also an area where multiple ethnic groups are represented. The Site is recognized as an Important Bird and Biodiversity Area (IBA) and is subject to a dedicated management plan.