The more natural the better! This is the main rule when evaluating the morphology of a body of water. Reeds growing on undisturbed shores, sandbanks and small islands in the water and branching streams meandering through undeveloped floodplains are signs of near-natural or ecologically valuable features. Many different species of fish and other aquatic animals also indicate a good quality of water.
Urban rivers and lakes, meanwhile, are a far cry from this, however. People have fortified their banks with concrete; they have added bridges, dams or embankments. Since 2000, however, the European Water Framework Directive has sought to ensure that EU countries restore water bodies to their original state. A Berlin example is the renaturation of the Panke, which has been freed from its concrete bed.
From 1999, water bodies were mapped comprehensively over several years. This involved the evaluation of aerial images and old maps, supplemented by onsite assessments. Seven classes ranging from 1 (unmodified) to 7 (totally modified) record how strongly the environment has been modified by humans.
As far as rivers and streams are concerned, the Kuhlake in the Spandauer Forst comes out on top with a score of 3.6. The Hellersdorfer Graben comes in last with a score of 6.9. The Spree has therefore been modified heavily and the Havel modified distinctively.
Lake shores, most of which fall into classes 3 and 4, are rather natural by comparison. The Havel surrounding the Pfaueninsel and the southern shore of the Müggelsee have only been modified marginally (2), for example.