Zirou lake was initially an underground lake, but a strong earthquake, approximately 10,000 years ago, caused the cave’s roof to collapse and created the magnificent landscape we see today. The lake is somehow connected to the Louros River that flows on the far side of the national highway, since both bodies of water have the same aquifer. The lake’s maximum depth is 70 meters (the depth near the rocky north shore is only nine meters) and the water temperature fluctuates from 9,6°C to 21,2°C, depending on the season. There are numerous prehistoric settlements in the wider region, so it is very likely that Zirou lake was visited by humans for thousands of years.