Llyn Cwm Llwch
It is drained by the Nant Cwm Llwch which empties into the Afon Tarell , which itself enters the River Usk at Brecon . 
<triplet> Afon Tarell <subj> River Usk <obj> mouth of the watercourse <triplet> River Usk <subj> Afon Tarell <obj> tributary <triplet> Brecon <subj> River Usk <obj> located in or next to body of water