The basin of the lower Kouilou river, lying a little to the west of Dimonika (CG004), is bordered to the south-west by the Atlantic coast, between Diosso and Madingo–Kayes, to the north-west and north by the road from Madingo–Kayes to Nkola and Magne, and to the east by the Lakes Kitina and Titina. The main part of the site is occupied by the 900 km² marsh of the Kouilou basin, which includes 15 km² of Rhizophora mangrove, 20 km² of lakes, 65 km² of papyrus (pure or mixed with low shrubs), 30 km² of wet Jardinea grassland, c.170 km² of flooded thickets (mainly Raphia, Pandanus, Ficus trichopoda) and c.600 km² of permanently or seasonally flooded forest (Chrysobalanus, Ctenolophon, Sacoglottis, Uapaca). The coastal strip is occupied by sandy beaches, evergreen thickets and dry evergreen Symphonia forest (in gorges), giving way to a forest-savanna mosaic further inland—with c.100 km² of dry Andropogon grassland. Semi-evergreen rainforest, from this mosaic to the foothills of the Mayombe, covers c.500 km². Most of the villages are located along the coast and the Madingo–Kayes road; there is also a cluster of fishing villages in the vicinity of Lake Nanga and small fishing camps on the Kouilou. The dryland forests are all exploited by selective logging. A large proportion of the grassland is being planted with Eucalyptus, an operation financed by Shell.
See Box and Table 2 for key species. A total of 378 bird species is known from the area, of which 284 are likely to breed (based on a five-month survey). Species of special interest include Sterna balaenarum, a non-breeding visitor to the coast in unknown numbers, but thought to be regular, Merops breweri whose breeding density on the forest-savanna ecotone is locally high, and Ploceus subpersonatus recently discovered in coastal bush. Extensive swamp-forest and thickets harbour good numbers of little-known species such as Tigriornis leucolophus, Canirallus oculeus and Scotopelia bouvieri. Pseudochelidon eurystomina is a common visitor from September to November and some may breed on occasion. In addition, two species of the Zambezian biome (A10), Lybius minor and Hirundo rufigula, have been recorded.
Non-bird biodiversity: Trichechus senegalensis (VU) is present in the Kouilou river and its larger tributaries (e.g. the Nanga), but is probably decreasing. Loxodonta africana (EN), Mandrillus sphinx (LR/nt) and small arboreal monkeys have been largely exterminated, but there are still good numbers of Gorilla gorilla (EN) and Pan troglodytes (EN).
BirdLife International (2020) Important Bird Areas factsheet: Lower Kouilou basin. Downloaded from http://www.birdlife.org on 05/04/2020.