The Yenisei, also written as Yenisey, is the largest river system flowing to the Arctic Ocean. It is the central of the three great Siberian rivers that flow into the Arctic Ocean. Rising in Mongolia, it follows a northerly course to the Yenisei Gulf in the Kara Sea, draining a large part of central Siberia, the longest stream following the Yenisei-Angara-Selenga-Ider river system. The upper reaches, subject to rapids and flooding, pass through sparsely populated areas. The middle section is controlled by a series of massive hydroelectric dams fuelling significant Russian primary industry. The maximum depth of the Yenisei is 80 feet and the average depth is 45 feet. The depth of river outflow is 106 feet and inflow is 101 feet.