The Afon Marteg is a river in Powys, Wales.
It is about long, flowing roughly south-west to join the Wye at Pont Marteg (grid reference SN952714) about above Rhayader.Ordnance Survey Landranger 1:50,000 map, sheet 136 or 147
Fishing is available, with appropriate permits, for brown trout, chub, dace, grayling and pike. The river has a run of spawning Atlantic salmon in the autumn.
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