The question of the origin of the Plitvice Lakes, situated in the Dynarics Mountains, in central Croatia is still unexplained. Not so many place in a literature is dedicated to this issue. It is said that the Plitvice Lakes are of tectonic or karst origin. In the article the complicated origin of the lakes is shown. To define their origin the author proposes the term “tectonic – barriered”. As a result of tectonical movements which occured on the researched area, many tectonic faults were formed. At the bottom of the lakes barriers of sedra – rock of biogenic origin started to grow. The process of sedra creating has been lasting till today and as a result a very complicated, permanently transformed lakes system has formed. At present, below the lowest located lake of the Plitvice Lakes new lakes appear, which demonstrate about existing and growing submarine barriers.