The problem

The fragmentation of rivers has resulted in a significant deterioration of biodiversity, water quality and natural habitats.

European rivers are the most fragmented in the world, which is negatively impacting biodiversity.

It is widely held that rivers support some of the Earth’s richest biodiversity and provide essential ecosystem services to society. Free flowing “open rivers” provide habitat for many species of plants and animals that depend on flowing water, deliver sediment that keeps deltas above rising seas, and provide nutrients to fertilise floodplains and create wetlands. However, when rivers become fragmented, their ecological status rapidly deteriorates. European rivers are the most fragmented in the world, and only one-third of its rivers have ‘good ecological status’, as defined by the EU Water Framework Directive.

Artificial barriers to river flow are the leading cause of river fragmentation. 

One of the biggest causes of river fragmentation is the presence of man-made barriers to river flow. In 2020, the EU-funded AMBER project estimated over one million barriers in rivers and streams across Europe, amounting to 0.74 barriers/km. This is having a catastrophic impact on biodiversity. The change in flow caused by dams can fundamentally impact habitats, potentially over thousands of miles. The main negative effects of dams include: 

  •  Deterioration of biodiversity: impeded fish migration can cause entire aquatic ecosystems to be deprived of sources of nutrients and trace minerals, negatively impacting the rest of the food chain. 
  • Deterioration in water quality caused by changes in temperature, oxygen content, the circulation of nutrients and, in some cases, toxic chemicals from the dam site.
  • Loss of habitat from changes in flow and sediment load: depleted flows downstream can affect coastal deltas. Rivers can become disconnected from their floodplains and wetlands. Dams can also undermine a river’s ability to provide natural flood control, increasing flooding during heavy rainfalls. In the face of escalating climate change, bodies of water that have moved away from their natural states will be more vulnerable to extreme events (e.g. severe flooding or periods of drought).