Nera (Danube) basin and it is not navigable. After the filling of the artificial Lake Đerdap, as a result of the Iron Gate I Hydroelectric Power Station which was finished in 1972, the mouth of the river into the Danube was flooded. In order to allow the optimal electricity production, the water level of the Nera at the mouth should not go below , while it must not exceed it if the flooding of the banks is to be avoided. Since the mid-1990s, there are significant problems in fixing the river's level, as the process is costly and complicated. In 2018, representatives
Enns (river) the Northern Limestone Alps and the Central Eastern Alps on an eastern trajectory through Styria, where it passes the Dachstein group at its southern side. Between Admont and Hieflau, it takes a turn to the North and passes through the Gesäuse, a gorge of a length of , where it penetrates the limestone of the Ennstaler Alpen. Flowing to the north from there on, it reaches the state of Upper Austria at the mouth of the Laußabach. North of Steyr, it forms the border between Upper Austria and Lower Austria (formerly also known as "Austria above the Enns" and "Austria