To the left is Llyn Cwmffynnon the source or head of the Nantygwryd river (originally Y Mymbyr), which flow into Llynnau Mymbyr at Capel Curig.
The river feeding the lakes is the Nantygwryd (or Nant-y-gwryd), which has its source at Llyn Cwm-y-ffynnon, also marked on maps as the Nant Gwryd, which is a tributary of the Afon Llugwy.