Llyn Geirionydd lies in a valley in North Wales where the northern edge of the Gwydyr Forest meets the lower slopes of the Carneddau mountains. The lake is almost a mile long and covers an area of 45 acres (180,000 m²), but is never any deeper than 50 ft (15 m) according to Jehu’s survey. The lake can be reached by car from Trefriw or Llanrwst in the Conwy valley, the lane passing through the hamlet of Llanrhychwyn, or from the road through the Gwydir Forest. Access is not particularly easy by either route, but this has not stopped the lake being the only one designated in Snowdonia to permit power boats and water skiing.