The Gauja River (estonian:Koiva jõgi; german:Livländische Aa) is a river in Vidzeme, Latvia. It is the only large river of Latvia that begins and ends its flow in Latvia. Its length is 460 km, of which 1/5 or 93.5 km are in the Gauja National Park. In this part, the Gauja River flows through a spacious ancient Gauja valley, which is 1 to 2.5 km wide, and the maximum depth near Sigulda is 85 m. The sandstone rocks on the banks of the Gauja and its adjoining rivers started forming 370 to 300 million years ago during the Devonian period.