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 (left), the Pyssa (left), the Mezenskaya Pizhma (right), the Sula (right), the Kyma (right), the Vashka (left), the Pyoza (right), and the Kimzha (left).