The Thyamis, also known as Glykys or Kalamas, is a river in the Epirus region of Greece. It flows into the Ionian Sea. The names of the Chameria region, as well as the former Cham minority, derive from the river's name. Thyamis in ancient Greece was mentioned by Pausanias as forming the boundary between Thesprotis and Kestrine.

Some Renaissance scholars believed that the English River Thames owed its name to the River Thyamis, as early Celtic tribes were thought to have migrated from the Epirus region to England. While this belief influenced the modern spelling of the English river's name, it is no longer regarded as credible.