The Siret or Sireth is a river that rises from the Carpathians in the Northern Bukovina region of Ukraine, and flows southward into Romania for 470 km before it joins the Danube. In ancient times, it was named Hierasus.

The following cities are situated along the river Siret, from source to mouth: Roman, Bacău and Galaţi.

The following rivers are the major tributaries to the river Siret:  Bârlad, Suceava, Moldova, Bistriţa, Trotuş, Putna and Buzău.

During July 2010, Gheorghe Flutur, president of Suceava judet, told the Mediafax news agency his region was one of the worst hit in the country in the morning of the 29th as he co-ordinated local flood relief work in his stricken county. Later that day the River Siret threatened to break through the dykes protecting the town of Sendreni, as locals and emergency services reinforced the dykes with truckloads of sandbags to prevent the river breaking out and flooding the town.