The Strymonian or Strymonic Gulf (Greek:Στρυμονικός Κόλπος, Strymonikos Kolpos), formerly known as the Gulf of Rendina, is a branch of the Thracian Sea—itself part of the Aegean Sea—lying east of the Chalcidice peninsula and south of the Serres regional unit. The official name is Orfano Gulf (Κόλπος Ορφανού).
The river Strymon empties into the gulf.
The largest towns of the Strymonic Gulf, with the administrative divisions:
Three mountains are the natural border of the Gulf, to the north-east Pangaio, to the north Kerdylio and to the south Stratoni.
Coordinates: 40°40′N 23°50′E / 40.667°N 23.833°E