The River Trothy is a river which flows through north Monmouthshire, in rural south east Wales. It is a tributary of the River Wye. The river rises on Campston Hill, northeast of Abergavenny. It flows southwards until Llanvapley, where it turns east. About 1/3 mi south of Monmouth the river joins the confluence of the River Wye and the River Monnow.