Bala Lake (Welsh: Llyn Tegid) was the largest natural body of water in Wales prior to the level being raised to help support the flow of the Llangollen Canal. It is 4 miles / 6.4 km long by a mile / 1.6 km wide) and is subject to sudden and dangerous floods. It is crossed by the River Dee and its waters are famously deep and clear. The town of Bala sits at its northern end and the narrow gauge Bala Lake Railway runs for several kilometres along the lake's southern shore.
Bala Lake has abundant pike, European perch, trout, eel and gwyniad. It also contains the very rare mollusc Myxas glutinosa - the Glutinous snail. According to legend the lake is inhabited by a monster known affectionately as Teggie.
Also according to legend, while the Dee itself flows into the lake, the waters never mix.
The lake now forms part of the River Dee regulation System and the level at its outflow is automatically controlled. Depending on flow conditions and the level of water in Llyn Celyn, water can flow either into the lake or out from the lake at the normal outflow point.
In the 1990s the lake suffered from blooms of blue-green algae which indicated a significant and worrying eutrophication of the lake. Subsequent investigative work by the Environment Agency and the establishment of a partnership approach with the water industry, the farming community and others has put in place a plan for reducing discrete and diffuse pollution inputs to the lake.
A number of companies provide kayaks, yachts and various other types of boats for rent to tourists. On holidays these services get very busy and forward booking is essential.