Plitvice Lakes National Park contains a series of beautiful lakes, caves and waterfalls. These have been formed by processes typical of karst landscapes such as the deposition of travertine barriers, creating natural dams. These geological processes continue today.
The Plitvice Lakes basin is a geomorphologic formation of biological origin, a karst river basin of limestone and dolomite, with approximately 20 lakes, created by the deposition of calcium carbonate precipitated in water through the agency of moss, algae and aquatic bacteria. These create strange, characteristic shapes and contain travertine-roofed and vaulted caves. The carbonates date from the Upper Trias, Juras and Cretaceous Ages and are up to 4,000 m thick. In order to maintain and preserve the natural characteristics of the lakes, the whole of surface and most of the subterranean drainage system has to be embraced by extending the original borders of the park. The new areas comprise layers of karstified limestone with dolomites of Jurassic age.
There are 16 interlinked lakes between Mala Kapela Mountain and Pljesevica Mountain. The lake system is divided into the upper and lower lakes: the upper lakes lie in a dolomite valley and are surrounded by thick forests and interlinked by numerous waterfalls; the lower lakes, smaller and shallower, lie on the limestone bedrock and are surrounded only by sparse underbrush. The upper lakes are separated by dolomite barriers, which grow with the formation of travertine, forming thus travertine barriers. Travertine is mostly formed on the spots where water falls from an elevation, by the incrustation of algae and moss with calcium carbonate. The lower lakes were formed by crumbling and caving-in of the vaults above subterranean cavities through which water of the upper lakes disappeared.