The River Gwendraeth is a river in Carmarthenshire in west Wales. It has two almost equal branches that have their confluence in their joint estuary. The Gwendraeth Fawr (Large Gwendraeth in Welsh) is surprisingly the smaller and has its source above Cross Hands whilst the Gwndraeth Fach (small Gwendraeth in Welsh} flows further to the north having its source abut 4 miles north of Cross Hands. The two branches follow almost parallel courses to the sea.
The valleys of both rivers flow through a mixture of modestly steep mining communities and through the verdant agricultural land of Carmarthenshire, The most notable place of interest is Kidwelly Castle perched above the estuary of the Gwendraeth Fach. The Gwendraeth estuary widens rapidly before joing with the estuaries of the River Tywi and the River Tāf to form a three brached estuary. To the south of the estuary are the great flat sands of Cefn Sidan and Pembrey, whilst across the estuary on the banks of the River Tāf is Laugharne famed for its association with Dylan Thomas.