tributary of the Elbe River, rising in the Fichtel Mountains (Fichtelgebirge) of Germany and flowing generally east and northeastward into the Czech Republic past Cheb, Karlovy Vary, Žatec, and Louny until it reaches the Elbe (Labe) River opposite Litoměřice. The river is 196 miles (316 km) long, and it receives the Teplá and Blšanka rivers from the south and the Chomutovka River from the north.