The Trotuș is a river in eastern Romania, a right tributary of the river Siret. It emerges from the Ciuc Mountains in the Eastern Carpathians and joins the Siret in Domnești-Sat near Adjud after passing through Comănești and Onești in Bacău County. The total length of the Trotuș from its source to its confluence with the Siret is 162 km (101 mi). Its basin area is 4,456 km2 (1,720 sq mi).