Siret River, river, rising on the eastern slopes of the Carpathian Mountains in western Ukraine and flowing generally southward about 360 miles (575 km) across eastern Romania to enter the Danube River west of Galați. Its upper course cuts longitudinally through a wide valley with a sinuous course; its lower course, like that of the Danube, is low and marshy. Of the seven major rivers that drain from the Eastern Carpathians into the Siret, the Bistrița provides the greatest volume and has hydroelectric stations. The Siret’s basin is 17,000 square miles (44,000 square km) in area. The river is navigable only by small craft.