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
River Rhondda 1970s the river has been steadily improving in quality largely due to the closure of all the coal mines and through the investment in sewerage and sewage treatment. River Rhondda The River Rhondda () is a river in the Rhondda Valley, South Wales which has two major tributaries; the Rhondda Fawr () and the Rhondda Fach (). The river has two major tributaries: the Rhondda Fawr and the Rhondda Fach (respectively, the "big" and "little" Rhondda). Despite these names, both tributaries are of similar length. Both valleys display the U-shape cross-sections typical of glaciated valleys, having been eroded during successive