Four major rivers, namely the Rusizi, Malagarazi, Malagarazi, Akanyaru and Ruvubu rivers, make up the bulk of the country's hydrological network; the first three are adjacent. Along the deep waterways, there is usually lush vegetation, a relic of the region's ancient vegetation. In several regions that are mostly overpopulated, the surrounding vegetation has given way to crops.

The rivers of the Rusizi plain are the only ones to have benefited from in-depth studies on the algae they contain (Ruhwa, Nyakagunda, Rusizi, Nyamagana, Muhira, Muhira, Kaburantwa, Kaburantwa, Kagunuzi, Mpanda and Mutimbuzi). Studies carried out on the Rusizi River alone and its tributaries indicate the presence of 218 species of Diatoms. These are species considered tropical or endemic to tropical Africa or rarely reported in the literature. The Rusizi, its tributaries and the Mutimbuzi proved to be very rich in Diatoms. In waters poor in major cations in the Rusizi plain, typical species have developed. In this range, mention may be made of species such as Navicula cryptocephala, Navicula schroiteri, Navicula mitica, Navicula viridula var. rostellata, Gomphonema parvulum, Gomphonema clevei, Gomphonema clevei, Synedra clevei, Synedra ulna, Synedra ulna, Synedra ulna, Achnanthes ulna, Achnanthes linearis, Achnanthes lanceolata, Achnanthes exigua, Nitzschia linearis, Hishna antzschia amphioxys, Pinnularia subcapitata, and Pinnularia dubitabilis.