Tufa barriers are the result of continuous sedimentation processes along natural thresholds.
As the water flows in thin layers over thresholds, it is splashed up.
This disturbs the chemical balance and causes precipitation of the carbonates, which then creates sedimentary deposits.
Since the water forms larger surfaces at these places, increased quantities of carbon dioxide (CO₂) are released.
Calcium carbonate is secreted in the form of microcrystals that are deposited, eventually creating tufa sediments (CaCO₃).
This phenomenon particularly occurs on abundantly available mosses, enabling better adherence of the crystals.

In the course of time, older barriers can be flooded by rising water levels since other barriers have outgrown the older ones.
400 years ago, there were two lakes in the place of today's Kozjak lake.
In the lowest third of the lake, at the level of Matijaševića draga, a crown of an underwater barrier that is 40 m high, is stretching 4 m below the water surface.
This barrier certainly formed a magnificent waterfall in the past.
The travertine barrier at the Kozjak bridges (at the current end of the Kozjak lake), however, grew faster.
Thus, 400 years ago two lakes merged in one.
That is why the greatest depths of Kozjak lake are in its lower basin (north from the little island).
Tufa barriers are the result of continuous sedimentation processes along natural thresholds. As the water flows in thin layers over thresholds, it is splashed up. This disturbs the chemical balance and causes precipitation of the carbonates, which then creates sedimentary deposits. Since the water forms larger surfaces at these places, increased quantities of carbon dioxide (CO₂) are released. Calcium carbonate is secreted in the form of microcrystals that are deposited, eventually creating tufa sediments (CaCO₃). This phenomenon particularly occurs on abundantly available mosses, enabling better adherence of the crystals.
In the course of time, older barriers can be flooded by rising water levels since other barriers have outgrown the older ones. 400 years ago, there were two lakes in the place of today's Kozjak lake. In the lowest third of the lake, at the level of Matijaševića draga, a crown of an underwater barrier that is 40 m high, is stretching 4 m below the water surface. This barrier certainly formed a magnificent waterfall in the past. The travertine barrier at the Kozjak bridges (at the current end of the Kozjak lake), however, grew faster. Thus, 400 years ago two lakes merged in one. That is why the greatest depths of Kozjak lake are in its lower basin (north from the little island).
Plitvice Lakes National Park