The territory of Slovenia mainly (, i.e. 81%) belongs to the Black Sea basin, and a smaller part (, i.e. 19%) belongs to the Adriatic Sea basin. These two parts are divided into smaller units in regard to their central rivers, the Mura River basin, the Drava River basin, the Sava River basin with Kolpa River basin, and the basin of the Adriatic rivers. In comparison with other developed countries, water quality in Slovenia is considered to be among the highest in Europe. One of the reasons is undoubtedly that most of the rivers rise on the mountainous territory of Slovenia. But this does not mean that Slovenia has no problems with surface water and groundwater quality, especially in areas with intensive farming.