The Fiesa meres were formed due to the digging of clay needed by the former brickworks. The smaller secluded fresh water mere is situated right beneath the slopes and is up to 6.5 m deep. The larger mere is deeper and filled with brackish water, for from 1963 it has been linked with the sea. With their banks overgrown with a wide belt of reed and other riparian plants, the meres offer a safe shelter to fish, marsh birds and especially to some twenty rare and endangered dragonfly species. Due to their great ecologic value they have been included in the list of the most important natural heritage in Slovenia and 1989 proclaimed a natural monument.