Basse vallée de l'Ouémé, lagune de Porto-Novo, lac Nokoué: A Major Protected Wetland Landscape

The site is best known for being Benin's largest and most significant wetland complex, linking a major West African river to the Atlantic through a chain of lagoons and a large shallow lake. It combines river floodplain, open lagoon waters, fringing mangroves and adjoining coastal sand ridges into a single hydrological system. It is also notable as a Ramsar-protected site and as the focus of Benin's 2020 World Heritage candidacy, which presents the area as a cultural landscape where traditional lakeside communities have helped maintain biodiversity through participatory stewardship.

The landscape is shaped by the meeting of a large West African river system with the Atlantic coastal plain. The Ouémé River, after leaving the interior, enters an extremely low-gradient floodplain where it breaches its banks seasonally before reaching Lake Nokoué, a broad shallow lake that acts as a buffer between the river and the sea. From Lake Nokoué, water flows onward through the Porto-Novo lagoon before finally discharging into the ocean.

Geologically, the surrounding territory reflects three dominant structures: the flat-lying plateaus of the Continental Terminal on either side, the elongated notch of the lower Ouémé-So basin that channels the floodplain southward, and a belt of coastal sand ridges known as the Ogolian and Holocene cordons that line the southern edge of the system. These formations together produce a shallow, gently sloping basin in which water spreads out and lingers, sustaining floodplain forests, open water, fringing mangroves and seasonally inundated grasslands.

As Benin's largest wetland, the site concentrates an unusually broad range of aquatic and semi-aquatic habitats within a connected system. The lower Ouémé floodplain is defined by seasonal inundation and silt deposition, supporting rich floodplain soils, gallery vegetation and patches of freshwater swamp. Lake Nokoué provides large expanses of shallow lake habitat, while the Porto-Novo lagoon marks the transition to more brackish conditions as the system approaches the sea.

Along the southern fringes, mangrove formations with species such as Rhizophora racemosa and Avicennia germinans colonize the tidal zone, while drier plateaus and sand ridges support terrestrial vegetation including Khaya senegalensis and Albizia ferruginea. The combination of river, lake, lagoon, mangrove and floodplain vegetation creates a layered ecological mosaic in which aquatic, semi-aquatic and terrestrial species coexist within a relatively compact geographical footprint.

The wetland's connectivity between freshwater, lagoon and mangrove environments supports a diverse and ecologically meaningful fauna. Primates such as the red-bellied monkey, Cercopithecus erythrogaster, find habitat in the wooded areas around the floodplain, while the lagoons and river channels host the West African manatee, Trichechus senegalensis, one of the region's most distinctive aquatic mammals.

Reptiles are well represented, including Nile crocodiles in suitable habitats. Among the ungulates, Walter's duiker (Philantomba walteri) reflects the continuing importance of forested and wooded habitat in sustaining less conspicuous wildlife. The site also supports rich fish populations and waterbird communities associated with West African coastal lagoons, though specific species lists are limited in the available source material.

The site is one of the most important protected wetlands in Benin and is formally recognized under the Ramsar Convention on Wetlands, giving it international standing as a wetland of significant ecological value. This designation reflects the site's exceptional size and the diversity of habitats contained within the lower Ouémé hydrological system, including river floodplain, a major lake, a coastal lagoon and fringing mangroves.

Conservation significance is closely tied to the hydrological function of the Ouémé River: the annual flood cycle replenishes nutrients, sustains water quality, refreshes aquatic habitats and underpins traditional fisheries. Recognition of the area as a cultural landscape, with a participatory role for local communities in maintaining biodiversity, is a central part of its conservation profile. In 2020, Benin submitted the site to UNESCO for inscription on the World Heritage List, underscoring both its natural and cultural values and its importance as a flagship landscape for wetland protection in the country.

The strongest points of distinction for this site are its scale and its ecological connectivity: it is the largest wetland in Benin and brings together a major river, a large shallow lake and a coastal lagoon in a single linked system. The Ramsar designation anchors its international conservation profile, while the 2020 World Heritage nomination reflects the recognition of the area as a cultural as well as a natural landscape.

The presence of long-established lake-side communities, including Ganvié on Lake Nokoué, and the role of traditional practices in maintaining biodiversity add a distinctive human dimension. Combined with the site's faunal richness, including manatees, primates and crocodiles, and its mangrove and floodplain vegetation, these qualities make the wetland a defining natural and cultural feature of southern Benin.