# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 3 River Rehabilitation
### Europe  
According to the Water Framework Directive, the RBMPs, revised every 6 years, must include the Programs of Measures for all the water bodies falling below Good ecological quality status. All member states reported basic measures to reduce diffuse pollution. Although many measures and volunteer actions from farmers focused on improving water quality, this has not been sufficient. Nonetheless, ammonium and BOD\({}_{5}\) decreased in European rivers from 1992 to 2018 (78% and 54% respectively) mainly as a result of improved waste-water treatment ([[https://www.eea.europa.eu/data-and-maps/data/waterbase-water-quality-icm](https://www.eea.europa.eu/data-and-maps/data/waterbase-water-quality-icm)]([https://www.eea.europa.eu/data-and-maps/data/waterbase-water-quality-icm](https://www.eea.europa.eu/data-and-maps/data/waterbase-water-quality-icm))). Reduced flows resulting from water abstraction and water retention by dams (with consequences for longitudinal connectivity) have become greater concerns and are worsened by climate warming, especially in southern Europe [353; 355; 355]. Therefore, the European Commission recommends elaborating Drought Management Plans. Water abstraction has been addressed by implementing controls and reviewing licenses which have improved conditions in some countries between the 1 st and 2 nd RBMP. Regarding hydromorphological pressures, the improvements have been minimal although many countries plan to install fish passages or remove barriers. In addition, other rehabilitation projects have been completed that were not included in the RBMP. The European Centre for Rivers Restoration (ECRR) is a 20 years old international network that synthesizes knowledge and supports the development of best practices for successful river rehabilitation and management. It focuses on ecological, physical, spatial, and management measures and practices. It also provides a Manual of River Restoration Techniques ([[https://www.therrc.co.uk/manual-river-restoration-techniques](https://www.therrc.co.uk/manual-river-restoration-techniques)]([https://www.therrc.co.uk/manual-river-restoration-techniques](https://www.therrc.co.uk/manual-river-restoration-techniques))), developed by the UK Rivers Restoration Centre. The European projects, RESTORE, REFORM and FORECAST, contributed to the River-Wiki database ([[https://restorerivers.eu/wiki/](https://restorerivers.eu/wiki/)]([https://restorerivers.eu/wiki/](https://restorerivers.eu/wiki/))), which is being continuously updated and currently includes 1325 river rehabilitation projects in 31 countries. Most cases reported are from northern Europe, especially from the UK (>700), but there are also many projects taking place in the Netherlands, France, Spain, Austria, Italy, and Denmark. Most measures applied are bank stabilization and reshaping, creation of fish passes, dam removals, secondary channels creation, and riparian vegetation plantings. Many projects address several problems simultaneously reflecting the co-occurrence of multiple stressors in most European rivers [355; 356; 357]. In some case studies, response variables are monitored such as macroinvertebrate, fish and macrophytes assemblages, hydromorphology and water chemistry, either before and/or after the rehabilitation actions. Yet, from the database of 1325 study cases, only 161 indicated that ecological monitoring was performed. Indeed, after two decades of WFD history in Europe, the procedure of rehabilitating rivers in Europe remains poorly standardized, with the effects of the measures on ecosystems and biodiversity being monitored in only a fraction of cases [358]. Although bioassessment increases the total cost of any rehabilitation project, it is still remarkable that the values of collecting such data are easily dismissed, particularly considering the high costs of rehabilitating rivers [359]. From the relatively few rehabilitation projects that have been monitored before and after the measures were implemented, valuable lessons have been learned.