In the lower reaches from Reutte, the softwood floodplain is the most common. In addition to willows, gray alder grows here in particular. Due to the flat area, but also due to the construction, calmer sections of the river can be found. During floods, sand and fine soil in particular are washed up. This creates good conditions for a true gray alder forest to develop. The Grauerlenau is a highly endangered habitat.