Limestone is the natural resource of the region. Such rocks are unadulterated here and serve as good raw material for producing lime and cement. Exploitation of aggregate by opencast mining started in 1860, leading to excavations up to 150 m deep and large slag heaps. Once closed, the quarry was filled with water. Currently, “Piechcin” Dive Centre operates there. The reservoir is unique on account of its perfectly clear water and on sunny days white lime rocks and the azure surface of the lake resemble the shores of Croatia.