The Krka River within the borders of Krka National Park is categorised as a Category I watercourse. Considering that this is a very sensitive area, a wastewater treatment plant was constructed on the left bank of the river at Skradinski Buk. The plant has third degree treatment, which degrades organic matter by about 80% prior to the release of the treated water. The plant became operational in 2006.

After the construction of the treatment plant, the Public Institute of Krka National Park permitted the companies HEP d.o.o. and Vodovod i odvodnja d.o.o. to subsequently also connect to the plant, which enabled the treatment of the wastewater of all water users on the left bank of the Krka River at Skradinski Buk. The laws of the Republic of Croatia and the EU Directives (91/271/EEC) prescribe the quality standards for wastewater prior to its release into the natural environment (sea, rivers, etc.).

The functioning of the plant is controlled daily. Water leaving the plant is sampled and analysed by the Public Health Institute of Split-Dalmatia County. Water samples must correspond to the requirements stipulated by the water use permit and to the prescribed values for the water.

A treatment plant is defined as a water structure with facilities used to purify the wastewater from the public drainage system prior to its release into a natural receptacle. Its functioning uses biological procedures (the same as in the natural environment) with active silt, in which microorganisms (usually bacteria), degrade organic matter in the water while consuming oxygen. In this way, organic carbon is removed from the wastewater, the concentrations of nitrogen and phosphorous compounds are reduced and the silt is stabilised. The success of the aerobic process for the biological cleansing of wastewater depends on the concentration of organic compounds and the concentration of microorganisms. The products of the process are silt, gas and purified waste water.

The Public Institute of Krka National Park is also planning to construct treatment plants at Roški Slap and at the Puljani Eco Campus.