The Ruki is a major river in the
Cuvette Centrale of the middle Congo River basin. The watershed covers about . The
drainage basin is almost entirely pristine lowland forest and swamp forest. As of 2020, 248 species of fish had been identified in 26 families. The main rivers are the Ruki-Busira, Momboyo-Luilaka,
Tshuapa,
Lomela and
Salonga. The most important town in the river basin is
Boende on the Tshuapa, upstream from where it joins the Lomela to form the Busira. The Ruki River forms above
Ingende where the
Momboyo River joins the
Busira River from the left and flows in a west-northwest direction. It enters the Congo from the east, flowing past the north of the town of
Mbandaka. The Ruki and its main tributary the Busira can be navigated year round, since the depth is always more than and reaches in the flood period. High water is in March-April and November. Low water is in February and June-July. The Ruki itself is just long, and extends downstream from the mouth of the Momboyo, which is above Ingende. Higher up it is called the Busira as far as the confluence of the Tshuapa and the Lomela. The Busira section is long, and the whole Ruki-Busira waterway is long. The Ruki-Busira receives four navigable tributaries: the Momboyo at from its mouth, the Salonga at , just upstream from
Lotoko, and the Tshuapa and Lomela which converge to form the river. ==Colonial period==