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 . Its basin area is .
Towns and villages
The following towns and villages are situated along the river Trotuș, from source to mouth: Lunca de Sus, Lunca de Jos, Ghimeș-Făget, Palanca, Agăș, Comănești, Dărmănești, Târgu Ocna, Onești, Adjud.
Tributaries
The following rivers are tributaries to the river Trotuș (from source to mouth):
Left: Gârbea, Valea Întunecoasă, Antaloc, Valea Rece, Bolovăniș, Tărhăuș, Șanț, Cuchiniș, Brusturoasa, Caminca, Șugura, Dracău, Agăș, Seaca, Ciungi, Asău, Urmeniș, Plopul, Larga, Cucuieți, Vâlcele, Gălian, Caraclău, Tazlău, Pârâul Mare
Right: Comiat, Bothavaș, Ugra, Boroș, Valea Capelei, Aldămaș, Popoiul, Ciugheș, Cotumba, Grohotiș, Sulța, Ciobănuș, Șopan, Uz, Dofteana, Slănic, Nicorești, Oituz, Cașin, Găureana, Gutinaș, Bogdana, Gârbovana, Căiuți, Popeni, Bâlca, Domoșița