The Mezen (Russian: Мезень) is a river in Udorsky District of the Komi Republic and in Leshukonsky and Mezensky Districts of Arkhangelsk Oblast in Russia. Its mouth is located in the Mezen Bay of the White Sea. Mezen is one of the biggest rivers of European Russia. It is 857 kilometres (533 mi) long, and the area of its basin 78,000 square kilometres (30,000 sq mi). The principal tributaries of the Mezen are the Bolshaya Loptyuga River (left), the Pyssa River (left), the Mezenskaya Pizhma River (right), the Sula River (right), the Kyma River (right), the Vashka River (left), the Kimzha River (left), and the Pyoza River (right).