Sedra (engl. tufa) u slatkovodnim ekosustavima nastaje dinamičnom interakcijom kemijskih i bioloških čimbenika te ovisi o elementima koji trebaju biti prisutni poput zasićenja vode kalcijevim karbonatom, odgovarajuće pH vrijednosti i niske koncentracije organske tvari dok će postojanje biološke komponente poput mahovina, algi kremenjašica i nekih beskralježnjaka također imati važnu ulogu u nastajanju sedrenih barijera. Plitvička jezera kao najveći i najstariji nacionalni park te područje iznimne prirodne vrijednosti uvršteno na Listu svjetske prirodne baštine UNESCO-a, upravo jedinstvenu univerzalnu vrijednost prepoznaje u sedrenim barijerama i procesu njihovog nastanka. Kaskadni jezerski sustav nastao je uslijed povoljnih uvjeta za taloženje kalcijevog karbonata (sedre). Rast sedrenih barijera ovisi i o hidrološkim prilikama, a nepovoljno djeluju erozijski procesi kao i promjene povezane s povećanjem koncentracije hranjivih tvari dušika i fosfora, a koje dovode do eutrofikacije. Proces osedravanja u kaskadnom sustavu Plitvičkih jezera nije ugrožen, ali svakako je nužno kontinuirano pratiti moguće promjene.. Tufa is formed in freshwater ecosystems by a dynamic interaction of chemical and biological factors. It depends on some elements that need to be present - water saturation with calcium carbonate, adequate pH value and low concentrations of organic matter, and the existence of a biological component, i.e. mosses, diatoms and some invertebrates that also play an important role in the formation of tufa barriers. As the largest and oldest national park and an area of ​​exceptional natural value, Plitvice Lakes was included in the UNESCO World Heritage List, whose unique universal value was recognized in its tufa barriers and the process of their formation. The cascade lake system was formed in conditions favourable for the deposition of calcium carbonate (tufa). The growth of tufa barriers also depends on hydrological conditions, and is adversely impacted by erosion processes and changes associated with increased nutrient concentrations (nitrogen and phosphorus), which lead to eutrophication. The tufa formation process in the cascade system of Plitvice Lakes is not endangered, although it is certainly necessary to continuously monitor any possible changes.