The Ohrid Lake is roughly 10 million years old, and is believed to be the oldest lake in Europe, and one of the deepest, at 288 meters. The lake is unique in that it is home to over 200 endemic species, which means that they can't be found anywhere else on the planet. Unlike other old lakes which have dried up since their creation, the Ohrid Lake has remained filled with water, largely due to the way it is fed. Most lakes are fed by rivers and streams, and eventually fill with sediment and become dried up. The Ohrid Lake is filled by underground springs, which are naturally filtered by the sand and soil, and therefore only pure, crystal-clear and sediment-free water is fed to the lake.
The water in the lake is so clean that many people fill water bottles from the deeper parts and drink it directly. The water that is fed from the underground springs is the purest water possible, and at some parts, you can even see the sand at the lake bed bubbling where the fresh water is entering the lake.