Much of southern Europe escaped glaciation thousands of years ago and hence diversity within water bodies tends to be higher here, than in northern Europe. In addition, the soft limestone that the Balkans are built of, allow water that seeps underground to create subterranean karst channels where many aquatic species live.
The ridge of the Balkan Range is the main watershed between the Black Sea and the Aegean. The deep karst bedrock provides a steady outflow of the underground aquifer feeding those rivers, and the sprawling old forests retain the topsoil moisture. The riverbeds are steep, the rivers are fast and abundant in water.
At many places these rivers jump off high cliffs, forming scenic waterfalls, which the local population calls praskala, or spray gushers. Central Balkan is the scene of some of the highest and most impressive waterfalls in Bulgaria, notably Raiskoto Praskalo (124.5 m.), Vidimskoto Praskalo (80 m.) and Kademliiskoto Praskalo (72 m.).
The Balkans region hosts an extremely diverse and highly endemic (both at a local and regional level) gastropod fauna (snail species), with about 200 known species. For example, the Sava River alone harbours 103 species, of which 54 are endemic. Many endemic fish species and genera are also present in the ecoregion.