Dorothea Quarry

Dorothea is a flooded slate quarry located between the villages of Talysarn and Nantlle in Gwynedd, North Wales. Slate was first extracted from the site around 1830 and the quarry was finally closed down in the 1960s. Since the pumps stopped the quarry slowly filled with water until it reached the natural water table. Dorothea has been a popular dive site ever since.

The depth of the quarry varies greatly and contrary to what many people hear there are many shallow areas that are suitable for snorkellers and beginner scuba divers. The deepest point is believed to be around 108m. Other underwater attractions include tunnels at 21m and at 56m. Generally the water is very clear but it can be cloudy around 0-10m at certain times of year. The temperature varies from 4-5°C in winter to 18-20°C during the summer months.