Tisza (tĭsˈə) [key], Serbian Tisa tēˈsä, Rus. Tissa or Tisa both: tĭsˈə, Ger. Theiss (tĪs), river, c.600 mi (970 km) long, formed by two headstreams in the Carpathians, W Ukraine. It flows generally S across E Hungary, past Szolnok and Szeged, into N Serbia, where it enters the Danube River E of Novi Sad. The Körös and Mureşul rivers are its chief tributaries. There are hydroelectric facilities on the river in Hungary. The Tisza is navigable for small craft to Szolnok and is also used to float timber.