protected area in Guinea-Bissau
Lagoas de Cufada Natural Park is in Guinea-Bissau.
Established in 2000, Lagoas de Cufada was the first protected area in Guinea-Bissau. Measuring 890 km (340 sq mi), it is the largest freshwater reserve in the country, and is classified as a "Ramsar Site - Wetland of World Importance". Chimpanzees are reported to live in the National Park, making nests in oil palms. Other animals found at the site include hippopotamus, waterbuck, roan antelope, African buffalo, leopard, hyena, African dwarf crocodile and around 250 bird species.
Guinea-Bissau is an extremely underdeveloped country and tourist infrastructure is scant, so you'll likely have to improvise on this one. There is at least one company online that offers tours. If you want to try your luck on your own, you can try contacting the Instituto da Biodiversidade e das Áreas Protegidas in Bissau and arrange visitation with them. Otherwise, get to Buba – there are signs advertising the park around town, and you should be able to find someone (e.g. at your hotel) to arrange a tour there.
You'll be touring by boat.