Even though the vegetation has beneficial effects for the formation of tufa, excessive concentrations of organic substances within the water have adverse effects on these formation processes. Excessive plant cover has adverse effects on mineral sedimentation. Down the Korana River from the Korana bridge, for example, travertine creation ends quite quickly, in spite of the supersaturation with calcium bicarbonate, because of the increased concentration of organic matter in the water. The park authorities have therefore begun systematic removal of excessive vegetation along the barriers. Water purity is the decisive factor for tufa formation. The water at the influx to the Plitvice Lakes is defined as pure from an analytical point of view. The Dissolved Organic Carbon (DOC) value of the water barely exceeds 2.5 mg/L at the influx to the Upper Lakes (Matica). At the Lower Lakes higher concentrations are measured (5.15 mg/L). At the springs of other Croatian rivers in the karst region similar concentrations have been recorded.
