The main causes of anthropogenic impacts on aquatic ecosystems include canalisation and drainage of floodplains, excessive nutrient inputs, water abstraction and dam construction. In the case of rivers, phosphorus inputs have been combated very well and water abstraction has also been reduced. As far as dam construction is concerned, renaturalisation measures are often difficult because dams are used for the supply of resources (e.g. drinking water) or for hydropower generation, two ecosystem services that are important for humans. Similarly, many of the former floodplains are now farmland, and many drainage systems and river courses have been preserved. However, there are renaturalisation projects to return floodplain areas to the river and increase the possibility of flooding in order to preserve floodplain forests and their organism communities. One such project was carried out in the Dahme near Staakmühle (municipality of Briesen, Brandenburg, Germany), where the erosion of the river bed caused by canalisation was counteracted by filling in gravel and a formerly cut off and dried up meander was excavated and reconnected to extend the flow length by about 130 m, thus reducing the gradient and erosion of the river. The meander was then allowed to erode its banks in the hope that the nearby woodlands would be flooded.
(https://www.feuchtwaelder.de/projekttagebuch/auenwaelder-brauchen-wasser.html)

In order to evaluate restoration projects, a clear statement of the expected restoration results is needed. Unfortunately, the objectives of ecosystem restoration are often not clearly defined and projects are rarely evaluated beyond the implementation of the restoration measure (mainly due to financial constraints), making it difficult to evaluate restoration success. In other cases, restoration objectives are defined, such as in the Dahme project for riparian forests, but additional impacts are not considered or monitored. In the case of a meander reconnection, the habitat in the river course is completely recreated and offers an opportunity for rapid colonisation by river life such as benthic macroinvertebrates. In addition, the implementation can create structures in the course of the river that no longer exist in other parts of the river ecosystem. In the case of the restoration of the Dahme, gravel was added to raise the riverbed and avoid initial erosion and incision, creating a heterogeneity of habitat for organisms in the river, as coarser sediments are virtually absent in the nearby sections of the Dahme. The impact of the restoration is thus likely to go beyond the stated objectives and we are in the process of assessing the impact of the restoration of the Dahme in the riverbed compared to a) a meander that has never been straightened but has undergone some bank stabilisation decades ago and b) the reference conditions established for the Dahme river type (river type 14 or 15, depending on the location along the Dahme).