Lake Ossa is 7 km (4.3 mi) wide at its widest point.

The lake complex was created by tectonic movements of the Earth's crust.

Common trees include azobe (Lophira alata), ndo’o (Irvingia gabonensis), African corkwood (Musanga cecropioides), afara (Terminalia superba) and iroko (Milicia excelsa).

There is a freshwater swamp forest at the southeastern end of the lake around the outflow channel, with the trees Pandanus, Raphia, Mitragyna, and Uapaca.

Lake Ossa is a popular site for recreational fishing, boating, and watersports.