The dried bottom of the Intermittent Lake Cerknica in the Karst region of Slovenia in summer. Due to its regular draining and filling, this lake had already attracted explorers as early as in the 17th century, and has been the object of study and admiration ever since. The vast lake reed beds provide shelter, food, and nesting grounds to a variety of water and other birds. The lake is a nesting ground for 94 different species, although more than 230 species have been observed in its vicinity. This makes Lake Cerknica an important ornithological location. In summer, Lake Cerknica is usually completely drained. When the water level drops, deep sinkholes are exposed underneath a thick layer of sediment.