The Niger Delta is an enormous classic distributary system located in West Africa, which stretches more than 300 kilometres wide and serves to capture most of the heavy silt load carried by the Niger River. The peak discharge at the mouth is around 21,800 cubic metres per second in mid-October. The Niger Delta coastal region is arguably the wettest place in Africa with an annual rainfall of over 4000 millimetres. Vertebrate species richness is relatively high in the Niger Delta, although vertebrate endemism is quite low. The Niger Delta swamp forests occupy the entire upper coastal delta. Historically the most important timber species of the inner delta was the Abura (Fleroya ledermannii), a Vulnerable swamp-loving West African tree, which has been reduced below populations viable for timber harvesting in the Niger Delta due to recent over-harvesting of this species as well as general habitat destruction of the delta due to the expanding human population here. Other plants prominent in the inner delta flood forest are: the Azobe tree (Lophira alata), the Okhuen tree (Ricinodendron heudelotii ), the Bitter Bark Tree (Sacoglottis gabonensis), the Rough-barked Flat-top Tree (Albizia adianthifolia), and Pycnanthus angolensis. Also present in its native range is the African Oil Palm (Elaeis guineensis)
There are a number of notable mammals present in the upper (or inner) coastal delta in addition to the near-endemic White-cheeked Guenon (Cercopithecus erythrogaster, VU), the Critically Endangered Niger Delta Red Colubus (Procolobus pennantii ssp. epieni), which primate is endemic to the Niger Delta is found in the inner delta. The Endangered Chimpanzee (Pan troglodytes) is also found in the inner delta. The limited range Black Duiker (Cephalophus niger) is fournd in the inner delta and is a near-endemic to the Niger River Basin. The restricted distribution Mona Monkey (Cercopithecus mona), a primate often associated with rivers, is found here in the Niger Delta. The Near Threatened Olive Colobus (Procolobus verus) is restricted to coastal forests of West Africa and is found here in the upper delta.
Some of the reptiles found in the upper coastal Niger Delta are the African Banded Snake (Chamaelycus fasciatus); the West African Dwarf Crocodile (Osteolaemus tetraspis, VU); the African Slender-snouted Crocodile (Mecistops cataphractus); the Benin Agama (Agama gracilimembris); the Owen's Chameleon (Chamaeleo oweni); the limited range Marsh Snake (Natriciteres fuliginoides); the rather widely distributed Black-line Green Snake (Hapsidophrys lineatus); Cross's Beaked Snake (Rhinotyphlops crossii), an endemic to the Niger Basin as a whole; Morquard's File Snake (Mehelya guirali); the Dull Purple-glossed Snake (Amblyodipsas unicolor); the Rhinoceros Viper (Bitis nasicornis). In addition several of the reptiles found in the outer delta are found within this inner delta area.
Five threatened marine turtle species are found in the mangroves of the lower coastal delta: Leatherback Sea Turtle (Dermochelys coricea, EN), Loggerhead Sea Turtle (Caretta caretta, EN), Olive Ridley Turtle (Lepidochelys olivacea, EN), Hawksbill Sea Turtle (Eretomychelys imbricata, CR), and Green Turtle (Chelonia mydas, EN).
Other reptiles found in the outer NIger Delta are the Nile Crocodile (Crocodylus niloticus), African Softshell Turtle (Trionyx triunguis), African Rock Python (Python sebae), Boomslang Snake (Dispholidus typus), Cabinda Lidless Skink (Panaspis cabindae), Neon Blue Tailed Tree Lizard (Holaspis guentheri), Fischer's Dwarf Gecko (Lygodactylus fischeri), Richardson's Leaf-Toed Gecko (Hemidactylus richardsonii), Spotted Night Adder (Causus maculatus), Tholloni's African Water Snake (Grayia tholloni), Smith's African Water Snake (Grayia smythii), Small-eyed File Snake (Mehelya stenophthalmus), Western Forest File Snake (Mehelya poensis), Western Crowned Snake (Meizodon coronatus), Western Green Snake (Philothamnus irregularis), Variable Green Snake (Philothamnus heterodermus), Slender Burrowing Asp (Atractaspis aterrima), Forest Cobra (Naja melanoleuca), Rough-scaled Bush Viper (Atheris squamigera), and Nile Monitor (Varanus niloticus).
There are a limited number of amphibians in the inner coastal delta including the Marble-legged Frog (Hylarana galamensis). At the extreme eastern edge of the upper delta is a part of the lower Niger and Cross River watersheds that drains the Cross-Sanaka Bioko coastal forests, where the near endemic anuran Cameroon Slippery Frog (Conraua robusta) occurs.