The Tretya River (Russian: Третья речка, also spelt alternativelly as Tret'ya or Tretaya) is a stream in the Beringovsky District of Chukotka Autonomous Okrug, Russia. It drains part of the southern Anadyr Lowlands (very flat with wetlands and tundra). It flows northeast and then northwest into the Anadyr Estuary (its mouth is the southernmost notch on the image on that page). To the east of the Tretya is the Avtatkuul' zakaznik protected area. To the south is the Tumanskaya River.
Belugas are common in its waters.