Until the last century, the Rusizi plain was a natural area that was barely disturbed by humans. Stanley, who visited the region in the 1875s, describes the plain as an inhospitable area, full of wild animals (buffalo, elephants, warthogs, etc.) and practically uninhabited, probably due to the abundance of tsetse flies, schistosomes, which are the source of various diseases.

Since the 1950s, the colonial authority had begun to install peasants and introduced crops such as rice, cotton, and coffee. Very quickly, these installations led to the degradation of the natural environment. Natural vegetation was thus almost completely destroyed while exterminating most large mammals.

Following the creation of the National Institute for Nature Conservation (INCN) in 1980, which became the National Institute for Environment and Nature Conservation (INECN) in 1989, the Rusizi Reserve was created, putting approximately 8,000 ha under protection. In 1990, the Rusizi Nature Reserve was declared a “National Park” with 2 parts separated geographically, the Palm Grove Sector and the Delta Sector.

The Delta sector, in contact with the north coast of Lake Tanganyika, is in a sense a semi-floodable extension of the coastal lake zone. It has an area of approximately 1000 ha. According to the IUCN protection categories, this area is now considered a Managed Nature Reserve with the following management objectives:

- vegetation management in order to promote an increase in the population of large mammals, reptiles and other animals;

- creation and maintenance of favourable conditions for populations of resident and migratory birds, both aquatic and terrestrial;

- maintenance of a breeding area for fish species in the northern part of Lake Tanganyika;

- reduction of the pollution of Lake Tanganyika by maintaining a vegetative carpet that purifies sediments;

- creation of favorable conditions for tourism and educational activities;

- sustainable exploitation of certain resources by the local population.

To achieve these objectives, a global knowledge of biological resources, both flora and fauna, and the ecological factors that control them is of paramount importance. It is with this in mind that this study is conducted as part of the Lake Tanganyika Biodiversity Project (UNDP — RAF/92/G32).

The study therefore focuses, on the one hand, on the Delta sector of the Park with the aim of establishing a map of the distribution of vegetation and fauna and, on the other hand, on the lacustrine coastal zone, to assess the state of biodiversity of fish fauna. The interactions between these two contiguous ecosystems and in interlocking places will be analyzed.

This work consists of 3 main parts. After this general introduction, the first chapter deals with the situation of the Rusizi Delta in its geographical, historical, hydrological and climatic conditions, in order to better understand the ecological conditions that prevail in the terrestrial and semi-floodable biotopes of the Park, and in the lake coastline.

In the second chapter, we review the flora and fauna in the Delta sector of the Park, i.e. in terrestrial and semi-floodable ecosystems. The third chapter deals with fish fauna in the coastal zone of Lake Tanganyika adjacent to the Park. In both chapters, we will focus on both biological inventories and the assessment of biological diversity. The work ends with a general conclusion.