Contrary to its reputation as a clean, renewable energy source, hydropower threatens biodiversity worldwide. As more than 80,000 small hydropower plants operate or are under construction worldwide, their impact on ecosystems raises urgent concerns among environmentalists and scientists. These expansive plants make huge environmental improvements in both the upstream and downstream locales. They do this through extensive water impoundment and periodic release, producing significant ecological changes.
Global data reveals that over 2,800 reservoirs with a surface area exceeding 10 square kilometers have fragmented rivers, disrupting natural habitats and the flow of aquatic life. The Kafue Gorge Hydroelectric Scheme in Zambia is an illustrative example of these changes. The scheme has now changed the flow regime which has affected the germination of several plant species in downstream areas. This alteration sets off a domino effect across local ecosystems.
The impacts of these hydropower developments go far beyond just acute environmental destruction. They impact aquatic species immensely, disrupting spawning cycles of some of our most important fish populations. The Yangtze River is an alarming warning of this pattern. The recently completed Three Gorges Dam has resulted in almost a 90% collapse of the annual fry of four major carp species. These kinds of abrupt transitions underscore the importance of a comprehensive reassessment of hydropower’s place in responsible, sustainable energy solutions.
The Ecological Impact of Hydropower Plants
Currently-operating hydropower plants make some of the most invasive changes to river ecosystems by drastically changing natural water flows. When waters are impounded or released on an unnatural schedule, the natural flow regime is broken, causing ecological cascades. These changes have the potential to directly impact species establishment and inundation tolerance of plant species in downstream floodplains. The Kafue Gorge Hydroelectric Scheme serves as an example of this issue. It has altered downstream conditions and prevented the unimpeded upstream colonization of native vegetation.
Beyond impacting growth of aquatic plants, hydropower plants play a critical role in altering thermal dynamics of river systems. In the warmer months, lower stretches tend to have cold-water sink reaches formed. During the cold months, they warm up from water released from the deep parts of reservoirs. The loss of natural seasonal temperature variation is one of the most important factors adversely affecting aquatic life. Aquatic species—particularly fish—require highly specific temperature regimes to thrive and reproduce.
Aquatic biodiversity declines as a consequence of these dam and habitat changes. Research indicates that tracked populations of migratory freshwater fish decreased by an average of 81% between 1970 and 2020. Damming is one of the leading forces pushing this scary trend to accelerate. As river habitats unravel and ecosystems change, fish species are put to extreme tests. It turns out they have greater difficulty existing in places that humans have heavily impacted.
The Risks to Fish Populations
Perhaps the most alarming impacts of hydropower are on fish species. Studies have shown as many as 1 in 5 fish either die or experience life threatening injuries when passing downstream through turbine blades. This risk is exacerbated when a series of hydropower plants are constructed on the same river, further stacking the odds against migratory species. The collective effects of these barriers can cause dramatic decreases in fish numbers, increasing the burden placed on aquatic environments.
Hydropower projects have had a huge impact on river systems. Consequently, the spawning period for many fish has been thrown off. The Yangtze River’s four large carp species experience delayed and shortened spawning seasons below the Three Gorges Dam. This combined shock has resulted in a major short-term loss of fry production. Now, the long-term survival of these key fish populations is imperiled.
Moreover, the impacts extend beyond just fish. Even with a huge 63-fold boost in available waterscape, the giant otter population at Balbina Dam in Brazil has barely doubled. This growth is still woefully inadequate. Previous wildlife impacts are due to increased scarcity of resources and less denning space. This unfortunate outcome illustrates how this type of hydropower project can do lasting damage to animals that rely on robust aquatic ecosystems to thrive.
A Call for Sustainable Solutions
The international demand for renewable energy is through the roof. To begin with, we need to address the true, hidden costs associated with hydropower development. Although many consider hydropower the environmentally friendly fossil fuel alternative, the environmental impact should be hard to ignore.
Ecological impacts
Rivers are the most fragmented and dramatically changing ecosystems on the planet. This creates grave risks to biodiversity. Therefore, it is incumbent upon policymakers and energy developers alike to find more sustainable alternatives that avoid harming our ecosystems.
In order to preserve aquatic ecosystems, sometimes we need to build fish passages. In tandem with the installation, we constantly work on optimizing turbine designs to minimize injury rates for migrating fish. Comprehensive environmental assessments should be conducted before the construction of new hydropower plants to evaluate potential impacts on local biodiversity.