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
San Joaquin River watershed's four largest cities: Fresno, Bakersfield, Stockton and Modesto. Seven major tributaries flow directly into the San Joaquin River, all of which run from the Sierra Nevada westwards into the main stem. In addition, some of the discharge of the Kings River also enters the San Joaquin directly (but seasonally) through a distributary. Of these, the Tuolumne River is the largest in any respect: longest, greatest drainage basin, and highest discharge. The Merced River is the second largest by length and drainage basin, but the Mokelumne River has a greater flow. Tributaries are listed below proceeding from the mouth upstream,