How human-made dams impact rivers

The lifeblood of our planet

How human-made dams impact rivers

The lifeblood of our planet: How human-made dams impact rivers

As the lifeblood of the planet, rivers are teeming with biodiversity. They support a wealth of wildlife and provide many benefits to humans. In Canada, we have over 8,500 named rivers, according to WWF-Canada, and are home to 20% of the world’s freshwater resources. The Mackenzie River is the longest river system in our country. Running through the Canadian Boreal Forest, it spans 4241 km and feeds over 50,000 lakes.

When healthy, rivers provide many critical ecosystem services that support humans and wildlife. They are vital habitat for freshwater fish, which are an important food source across the world. They also pick up sediment (rocks, sand, and other solid materials) along the way and transport it downstream. Once settled, this material is transformed into alluvium, which is rich in topsoil according to the National Geographic. As it is deposited along river flood plains, it makes these areas incredibly fertile and important barriers for extreme flooding. Sediment delivered by rivers also ensures deltas remain above rising seas.

Fish leaping from river as it swims upstream
Photo by Drew Farwell on Unsplash

The Impact of Dams

Despite their importance, just a third of the world’s 246 longest rivers remain free flowing. A team of researchers from McGill University, World Wildlife Fund (WWF), and several other institutions discovered this finding while conducting a global assessment of rivers. The main reason for this fragmentation are human-built dams and reservoirs. These physical barriers can impact the seasonal flow of rivers, trap sediment, and also block the migratory paths of wildlife—an issue that is highlighted in our Biodiversity Action Agenda. They can even transform a river’s ecosystem from “cold, flowing and connected, to one that’s warm, stagnant and fragmented,” according to Guardian. Since 1970, wildlife populations in freshwater ecosystems have plunged by an average of 83%. This is largely due to pollution, overuse, and most notably, dams. Disney’s latest blockbuster, Frozen 2, even addresses the negative impact that dams can have on the environment.

Dam with flowing water
By Austin Evans on Unsplash

The global fight against climate change is centered on reducing the burning of fossil fuels and transitioning towards renewable energy. This shift is accelerating demand for low-carbon hydropower, such as dams. However, the environmental costs of these projects are often overlooked. Currently, there are a total of 60,000 large dams worldwide with 3,700 currently in the planning and construction phases. While rising temperatures have already impacted river biodiversity, this shift towards dams will degrade them further.


However, solutions shouldn’t hinge on the elimination of development, according to a lead author from the study. Rather, it’s all about finding sustainable steps forward that foster co-existence between humans and free-flowing rivers. Improving dam operations and finding more suitable locations that consider environmental impact are important measures. Shifting towards solar and wind projects can also be viable and sustainable alternatives. However, global cooperation and action are important as well. And the good news is that the international community has committed to “protecting and restoring” rivers as outlined in item 6.6 in the 2030 Agenda for Sustainable Development.