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 (the other two being the Ob River and the Lena River). 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.