Detail of naturally-formed tufa dam. A series of these dams retain the large lakes that spread throughout Plitvice Lakes National Park. Tufa is a type of limestone, formed by the precipitation of carbonate minerals from water. Here moss {Cratoneuron commutatum, Bryum ventricosum) is continually being encased in calcium carbonate deposits, gradually adding to the mass of the tufa dam over which the waterfall flows. Plitvice Lakes National Park, Croatia. November.