Large rivers like the River Rhine will take more than twelve years to recover enough for salmon to live there again, due to their isolation and distance between potential colonizers. Smaller streams recover faster after restoration than big rivers. Two restoration projects in Germany showed that small streams can recover benthic macroinvertebrate fauna relatively quickly, while a more isolated stream in the Upper Rhine valley did not fully recover within five years. This suggests that restoring a large river like the Rhine, which has lost many species and is more isolated, will take longer than twelve years to significantly improve.