At the end of Lake Grimsel extends in the wide valley arc the glacier forefield of the Lower Unteraar glacier. The young river Aare, fed with turbid glacier water runs its course from the glacier snout to the Lake Grimsel and designs the terrain in changing ways: differently winded watercourses, river terraces, sand and gravel banks arise again and again. Depending on day and year, the outflow of the glacier and the Aare change their shape: once it is a small glacial brook, otherwise a tearing meltwater stream. In areas that have been free of ice for long time and have not been permanently flooded, the first pioneer plants could colonize, like fireweed, toadflax and various willow species. They form a diverse mosaic of plant communities in the glacier forefield habitat.