The Tazlău is a left tributary of the river Trotuș in Romania. Its source is in the Tarcău Mountains. It discharges into the Trotuș in Slobozia, near the city Onești. The , which failed in 1991, was built on the river Tazlău. The following villages are situated along the river Tazlău, from source to mouth: Tazlău, Frumoasa, Balcani, Ludași, Pârjol, Tărâța, Hemieni, Scorțeni, Tescani, Berești-Tazlău, Sănduleni, Livezi, Helegiu and Slobozia. Its length is 89 km (55 mi) and its basin size is 1,104 km2 (426 sq mi).