Bala Lake ([ˈbala]; Welsh: Llyn Tegid, [ˈɬɨ̞n ˈtɛɡɨd]) is a large lake in Gwynedd, Wales. It was the largest natural body of water in Wales prior to the level being raised by Thomas Telford to help support the flow of the Ellesmere Canal. It is 4 miles (6.4 km) long by 1 mile (1.6 km) wide, and is subject to sudden and dangerous floods. The River Dee runs through it and the waters of the lake are famously deep and clear.