The River Gavenny or sometimes the Gavenny River is a short river in Monmouthshire in south Wales. It rises 1 mile (1.6 km) southwest of the village of Llanvihangel Crucorney from springs near Penyclawdd Court, supplemented by springs in Blaen-Gavenny Wood and tributary streams there and within the Woodland Trust-owned Great Triley Wood. It flows south for about 4 miles (6.4 km) to its confluence with the River Usk towards the eastern end of Castle Meadows at Abergavenny. The town derives its English-language name from the Gavenny's confluence with the River Usk. Of the buildings on the banks of the river, the Gothic Decorated style church of St Teilo at Llantilio Pertholey is especially notable. Parts of the church date from the thirteenth century with multiple additions since. Blaengavenny Farm, the name of which signifies the 'head of the Gavenny', is a sixteenth-century farmhouse near the river's source.

The River Usk rises on the northern slopes of the Black Mountain, Wales, in the westernmost part of the Brecon Beacons National Park. Initially forming the boundary between Carmarthenshire and Powys, it flows north into Usk Reservoir, then east by Sennybridge to Brecon before turning southeast to flow by Talybont-on-Usk, Crickhowell and Abergavenny, after which it takes a more southerly course.