This aquarium shows a travertine barrier, i.e. waterfalls. Fish from the family of trout live in such locations, but also from the family of carp, perch and others since tufa is found in several fish zones. Karst water contains a lot of dissolved limestone, which is a sedimentary rock formed by deposition of organic residues. Limestone mostly consists of a mineral calcite which is by chemical composition calcium carbonate CaCO3. In favourable conditions carbon dioxide is released from water and the mineral calcite is extracted. Calcite crystals are deposited with the help of travertine builders and sometimes in the river bed create tufa, a
porous and soft “flowing rock”. Travertine builders are living organisms, among which are bacteria, algae and moss. However, animal species also participate in the formation of travertine barriers, primarily molluscs and caddisflies. Limestone extracted from water is accumulated in travertine building organisms during their lives, which is deposited after the travertine builders die and decompose. Due to their role in formation, tufa is also called a “living rock". Their accompanying vegetation, molluscs, caddisflies and other fauna joined with plant communities, make habitats on tufa places with abundant fish food. Hollow places and canals in the submerged parts of travertine sediments are favourite natural shelters for fish and crabs.
Protection of tufa is important for the conservation of ecosystems of karst rivers. If a man changes conditions in the environment, tufa growth may be stopped.