How invasive species and dams are impacting river biodiversity

The lifeblood of our planet

How invasive species and dams are impacting river biodiversity

The lifeblood of our planet

How invasive species and dams are impacting river biodiversity

Rivers provide many important services for humans and wildlife. However, a recent study discovered that the biodiversity of over 50% of rivers worldwide has been seriously impacted.

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 silt) along the way and transport it downstream. As sediment is deposited along river flood plains, it makes the soil in these areas incredibly fertile and creates the conditions for fruitful agriculture. And of course, rivers zig-zag throughout all provinces and territories and deliver freshwater to Canadians and wildlife alike.

Grizzly bear with fish in mouth in river
Photo by DAPA images via Canva

The Impact of Dams and Invasive Species

As it turns out, the biodiversity of over 50% of the world’s rivers has been seriously impacted by human activities. The 2021 study that unearthed this unsettling statistic points the finger at river fragmentation, including dams, and the introduction of non-native fish species. Even more shocking, it was found that only 14% of rivers have managed to evade the detrimental impacts of these two culprits. As dams break up fish habitat and rich, native fish diversity is overrun by a few dominant invasive species, both rivers and humans face troublesome repercussions. After all, the ecological integrity of rivers is tied to human and wildlife health.

It may come as no surprise that the rivers of North America and western Europe have experienced the brunt of biodiversity loss. It is a well-established pattern that areas with a more affluent demographic and higher populations have a larger environmental toll.  As the study lead researcher, Sébastien Brosse told The Guardian, “There has been an increase in water quality in western European and North American rivers in recent decades, but I’m not sure the speed of change is sufficient because there has been a really steep decline in fish populations.”  

Salmon swimming upstream
Photo by mrbfaust from Getty Images Signature/Canva

With river fragmentation as a lead cause of declining river health, it is important to note that just a third of the world’s 246 longest rivers remain free-flowing. In 2019, 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 reasons 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 2019  blockbuster, Frozen 2, even addresses the negative impact that dams can have on the environment.

Human-made river dam
Photo by Austin Evans on Unsplash


The global fight against climate change is centred 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. As of 2019, there were a total of 60,000 large dams worldwide with 3,700 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 McGill Study. Rather, it’s all about finding sustainable steps forward that foster coexistence 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 committed to “protecting and restoring” rivers as outlined in item 6.6 in the 2030 Agenda for Sustainable Development developed by the United Nations.