The Environmental Impact of Damming Rivers

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Dams have long been hailed as marvels of engineering, providing hydroelectric power, flood control, and water storage for irrigation. However, the environmental consequences of damming rivers are increasingly becoming a matter of concern. This article will delve into the negative impacts of dams on river ecosystems, the broader biosphere, and human communities.

river dam

Key takeaways

  1. Damming rivers can have negative impacts on ecosystems and human communities.
  2. Dams can cause irreversible harm, including the extinction of species and displacement of communities.
  3. Balancing the benefits and drawbacks of dams is crucial for sustainable development.

Direct Impact of Dams on Rivers

Dams can damage rivers in multiple ways, leading to a wide range of adverse effects on ecosystems and their inhabitants.

Blocking Fish Migration

Dams create physical barriers that obstruct the passage of migratory fish, such as salmon and eel, which need to travel between freshwater and marine habitats to complete their life cycles. The construction of the Grand Coulee Dam in Washington State, for example, led to the extinction of several salmon populations in the upper Columbia River.

Slowing Rivers and Altering Habitat

The impoundment of water behind a dam slows down the river flow, creating a reservoir. This transformation from a fast-flowing river to a stagnant reservoir can lead to habitat loss for species adapted to living in flowing water. The Three Gorges Dam in China has significantly altered the habitats of the Yangtze River, endangering the critically endangered Yangtze River dolphin. the Yangtze River Contamination is currently a bigger issue though.

Trapping Sediments

Dams trap sediments that would otherwise be transported downstream, depriving habitats and ecosystems of crucial nutrients. The construction of the Aswan High Dam in Egypt has led to a reduction in sediment flow to the Nile Delta, contributing to the erosion of coastal wetlands and the decline of local fisheries.

Impacting Water Quality

Dams can also negatively affect water quality. The stagnant water in reservoirs can lead to the growth of harmful algae blooms, which can be toxic to humans and wildlife. Additionally, the altered temperature and oxygen levels in reservoirs can affect the survival of sensitive aquatic species.

Sustained Environmental Impacts

Beyond the immediate vicinity of dams, their impacts can be far-reaching and long-lasting, affecting entire ecosystems and communities downstream.

Alteration of River Flow and Sediment Transport

Dams can drastically change the timing and quantities of river flow, impacting aquatic and riparian life. For instance, the Colorado River has experienced significant ecological changes due to the numerous dams built along its course, resulting in the loss of native fish species and the spread of invasive species.

Colorado river
Colorado river

Lowering Groundwater Tables

The deepening of riverbeds caused by dam construction can lead to a lowering of groundwater tables along the river, reducing water accessibility for plant roots and human communities. As a result, farmers may experience reduced crop yields, and communities may face water shortages.

De-watering River Reaches

Dams can lead to the complete de-watering of certain river sections, causing devastating impacts on the species that inhabit these areas.

Erosion and Infrastructure Threats

Erosion of riverbanks and beds downstream from dams can undermine structures and woodlands, posing risks to both the environment and human-made infrastructure.

Reduced Spawning Habitat

The lowering of riverbeds caused by dams reduces the available habitat for spawning fish and invertebrates, threatening their populations and the ecosystems they support.

Damming Rivers: A Climate Change Conundrum

Greenhouse Gas Emissions

Although dams generate clean, renewable energy, their reservoirs can produce significant amounts of greenhouse gases, particularly methane. Decomposing organic matter in the reservoirs releases these gases, contributing to global warming.

AI-generated colossal dam
AI-generated colossal dam

Impact on River Temperature

Dams also affect river temperature, which can have consequences for the ecosystems downstream. The release of cold water from the dam can lower the overall temperature, disrupting the life cycles of fish and other aquatic species sensitive to temperature changes.

Climate Change Adaptation

On the flip side, dams can play a role in climate change adaptation by providing water storage during droughts (see also the impact of droughts on rivers) and helping to mitigate flood risks associated with extreme weather events. With the increasing frequency and intensity of such events, dams may become crucial tools in the fight against climate change.

Balancing the positive and negative impacts of damming rivers in the context of climate change is essential for developing sustainable strategies that prioritize both human needs and environmental preservation.

climate change impact on rivers
Climate change and rivers

Unmitigable Impacts of Large Dams

Some impacts of dams cannot be mitigated, resulting in irreversible harm to ecosystems and human communities.

Extinction of Fish and Aquatic Species

Dams can lead to the extinction of fish and other aquatic species by blocking their migration routes and disrupting their habitats. For example, the construction of the Balbina Dam in Brazil led to the extinction of several endemic fish species in the Uatumã River.

Disappearance of Birds in Floodplains

Dams can also have devastating effects on bird populations. Floodplain habitats, which are crucial for many bird species, can be lost due to altered river flow and sedimentation caused by dams. The Kakadu National Park in Australia has experienced a decline in waterbird populations as a result of altered flood patterns caused by upstream damming.

Loss of Forests, Wetlands, and Farmland

The construction of large dams and their associated reservoirs can lead to the loss of vast areas of forests, wetlands, and farmland. The Itaipu Dam on the border of Brazil and Paraguay, for example, flooded an area of more than 1,350 square kilometers, submerging critical ecosystems and displacing thousands of people.

Erosion of Coastal Deltas

Dams can contribute to the erosion of coastal deltas by trapping sediments that would otherwise flow downstream and replenish the delta. The Mississippi River Delta in the United States has experienced significant land loss due to sediment starvation caused by upstream dams and levees, making the coastline more vulnerable to storm surges and rising sea levels.

River delta, Alaska
River Delta, Alaska

The Human Cost of Damming Rivers

The construction of dams often results in the displacement of human communities, as homes and farmland are submerged or rendered uninhabitable.

Forced Relocation and Livelihood Disruption

When people are forced to leave their homes due to dam construction, they may lose not only their houses but also their livelihoods. The Sardar Sarovar Dam in India, for example, has displaced tens of thousands of people, many of whom were subsistence farmers or fishers who have struggled to find new sources of income.

Past Failures and Current Efforts in Resettlement

In the past, resettlement plans have often failed to provide adequate compensation and employment opportunities for displaced people. However, there are ongoing efforts to develop better resettlement plans that protect people’s rights and provide fair compensation and employment opportunities. The World Bank’s guidelines on involuntary resettlement are one example of an attempt to improve the situation for those affected by dam construction.

Table of the top 20 biggest dams in the world, sorted by their reservoir size

Dam NameReservoir Size (km²)Year BuiltCountry
Bratsk Dam5,5401967Russia
Guri Dam4,2501986Venezuela
Cahora Bassa Dam2,7381974Mozambique
Robert-Bourassa Dam2,8001981Canada
La Grande-2-A Power Station2,1331992Canada
Zeya Dam2,4201978Russia
Tucuruí Dam2,4301984Brazil
Krasnoyarsk Dam2,0001972Russia
W.A.C. Bennett Dam1,5501968Canada
Daniel-Johnson Dam1,5811968Canada
Itaipu Dam1,3501984Brazil/Paraguay
Three Gorges Dam1,0452012China
Nuozhadu Dam0.862012China
Ertan Dam0.851999China
Longtan Dam0.902009China
Grand Coulee Dam1,1621941United States
Sayano–Shushenskaya Dam0.621985Russia
Hoover Dam0.641936United States
Deriner Dam0.552012Turkey
Xiluodu Dam0.652013China

Positive Environmental Impacts of Damming Rivers

Flood Control

One of the primary benefits of dams is their ability to control floods. By regulating water flow, dams can help prevent catastrophic flooding events that can damage ecosystems, property, and human lives.

Water Storage

Dams can store water during wet seasons, ensuring a steady supply for irrigation, drinking, and other uses during dry periods. This can be beneficial for both humans and wildlife, providing a more stable water resource in arid or drought-prone regions.

Recreation and Tourism

In some cases, the reservoirs created by dams can serve as popular recreational areas for boating, fishing, and swimming. This can lead to increased tourism, providing an economic boost to local communities and fostering an appreciation for the surrounding natural environment.

Renewable Energy Production

Dams can play a significant role in generating renewable energy through hydropower. Hydropower is a clean, reliable, and sustainable energy source that produces electricity by harnessing the kinetic energy of flowing water. This reduces reliance on fossil fuels, thereby lowering greenhouse gas emissions and mitigating the impacts of climate change.

The Future of Damming Rivers: To Continue or Not?

As the global demand for energy and water resources continues to grow, the debate surrounding the future of damming rivers intensifies. On one hand, dams provide renewable energy, flood control, and water storage. On the other, they cause significant environmental and social consequences. Balancing these conflicting needs presents a complex challenge.

The future of damming rivers may lie in finding innovative solutions, such as developing smaller, environmentally-friendly dams, improving existing infrastructure, or exploring alternative energy sources. Striking a balance between the benefits and drawbacks of dams will require careful planning, collaboration, and a commitment to sustainable development.


What happens to a river when a dam is removed?

When a dam is removed, the river undergoes a process known as “river restoration.” Sediment trapped behind the dam is released, allowing the river to naturally reshape itself over time. Aquatic life, particularly migratory species, can then return to their original spawning habitats, often leading to an increase in biodiversity.

Which is the most heavily dammed nation in the world?

China holds the title of the most heavily dammed nation in the world. With tens of thousands of dams, including the world’s largest, the Three Gorges Dam, China leads in both quantity and scale of dam infrastructure.

What are the benefits of removing dams?

Removing dams can restore river ecosystems, leading to the return of native fish and other aquatic species. It can also improve water quality and reestablish natural sediment and nutrient flow. Moreover, dam removal often enhances recreational opportunities like fishing, boating, and hiking, fostering local economies (see also United Nations University Institute on Water, Environment and Health (UNU-INWEH))

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Author: Richard
Meet Richard Buettner, the esteemed editor of GeoAffairs, armed with a Master's degree in Geography and sharing his valuable insights through 25 years of dedicated experience in the field.

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