Even after more than a century of ichthyological research in the Congo basin, many rivers still remain almost terra incognita . The ichthyofauna of the rivers of the Kahuzi-Biega National Park (KBNP), a UNESCO World Heritage site, is no exception to this. Two major right bank affluents of the Congo flow through this park, i.e. the Luka (Lowa basin) in the northern and the Lugulu (Ulindi basin) in the south-western part of the park. A first overview of the current knowledge of the ichthyofauna of the region has been compiled based on the RMCA collection holdings from: (1) the Luhoho (headwater stream of the Lowa basin), (2) the downstream Lowa affluents and (3) recent collections (2009-2010) from the Lowa River itself. Unfortunately, data for the Luka and Lugulu, both situated inside the park, are missing. A total of 6 families, containing 12 genera and 24 species have been identified from the Luhoho basin near the northeastern border of the KBNP. With 12 species, Cyprinidae is the most species rich family followed by Amphiliidae (5) and Mochokidae (3). The downstream affluents of the Lowa harbour 15 families containing some 42 genera and, at least, 38 species as specimens of about 18 genera have not yet been identified up to species level. Here, Alestidae (8) appear to be most species rich followed by Claroteidae (7) and Cyprinidae (6). Finally, 10 families, containing 18 genera and 19 species, including a new Marcusenius species, are found in the Lowa River with both Mormyridae (4) and Cyprinidae (4) being the most species rich families. Respectively 18 (75%), 31 (82%) and 17 (89%) species are unique for each of these Lowa basin stretches. These observations probably do not simply reflect longitudinal patterns by distance but rather isolation by waterfalls.