A turlough is a limestone feature, a seasonal lake that has no feeder or outlet streams but instead relies on fluctuations of the water table. Sometimes they are full of water, sometimes they are dry. The one at Pant Llyn can cover a few acres and up to eight feet deep, sometimes a just a dry hollow. The name Pant Llyn translates to ?Lake Hollow?. They are very rare, a few in Ireland but the one at Pant Llyn is the only one on the British mainland. The development at Cilyrychen, a large disused limestone quarry, is very close, and with seven days a week heavy wagons in and out would undoubtedly pollute the water table,