Llyn Tegid was formed during the last Ice Age when glaciers blocked the valley of the River Dee with debris. The resulting rectangular lake is 4 miles long, three-quarters of a mile wide and, in places, over 42m deep.
Local folk tales record an alternative to the glacial version of events. Once upon a time the valley was home to a cruel and dissolute prince named Tegid Foel. One night the harpist at a banquet thrown by the prince kept hearing a small bird urging him to flee the palace. He did so, fell asleep on a hilltop, and awoke at dawn to find the palace and principality drowned beneath the lake.
