The source of the Ruhr is near the town ofWinterberg in the mountainousSauerland region, at an elevation of approximately 670 metres (2,200 ft). It flows into the lowerRhine at an elevation of only 17 metres (56 ft) in the municipal area ofDuisburg. Its total length is 219 km (136 mi), its average discharge is 79 cubic metres per second (2,800 cu ft/s) atMülheim near its mouth. Thus, its discharge is, for example, comparable to that of the riverEms in Northern Germany or theRiver Thames in theUnited Kingdom.
TheRuhr area was Germany's primary industrial area during the early- to mid-20th century. Most factories were located there. Theoccupation of the Ruhr from 1923 to 1924 by French forces, due to theWeimar Republic's failure to continue paying reparations fromWorld War I, provokedpassive resistance, which saw production in the factories grind to a halt. As a result, the Germanhyperinflation crisis grew even worse.
DuringWorld War II, two of the dams on the Ruhr, theMöhne Dam and theSorpe Dam were targets forOperation Chastise, in which special "bouncing bombs" were developed to take out the dams and flood the valley, with the hope of seriously affecting the German industries there. The story was told in a 1951book and the popular 1955 film made from it,The Dam Busters.
The Ruhr was extensively used by adjacent factories for cooling-water and was heavily contaminated by industrial discharge in the 19th and 20th century, with significant negative impact. Large sections of the river were straightened, changing the habitat of the river and it's shore significantly. This led to a decline in various fish species, particularly the brook trout and related salmonids.
The establishment of dozens of smaller and larger dams largely prevented migratory species like salmon and theEuropean eel from ascending or descending the river as part of their lifecycle. Salmon have not been observed in the river in decades. Stocks of the European eel have dwindled. Both eel and brook trout stocks rely heavily on release of juveniles as part of conservation efforts.
Since 2013, the district government ofArnsberg, funded partially by grants of the European Union[2], is investing heavily into renaturation efforts to restore the natural river & habitat surrounding it. This includes various aspects, most significantly the removal or addition of bypasses to barriers such as dams along the whole river, to re-enable natural fish migration. Additionally, the river bed is widened substantially in sections, reducing the depth of the river and slowing down the flow of water, to enable natural reproduction of native fish, insects, etc.
Two sections of the renaturation have been completed (in Wickede & Witten)[2] with two more projects currently underway. 18 additional projects are still in planning stages and as of now, the river is not fully passable for migratory fish.
