High Quality Content by WIKIPEDIA articles! Llyn Cowlyd is the deepest lake in North Wales. It lies in the Snowdonia National Park on the edge of the Carneddau range of mountains, at a height of 1,164 feet (355 m) above sea level. The lake is long and narrow, measuring nearly 2 miles (3 km) long and about a third of a mile (500 m) wide, and covers an area of 269 acres (1.1 km2). It has a mean depth of 109 feet (33 m) and at its deepest has given soundings of 229 feet (70 m), this being some 45 ft (14 m) greater than its natural depth, the water surface having been raised twice by the building of dams.