Site icon Conservation news

Proposed Andean headwater dams an ecological calamity for Amazon Basin

Article by Liz Kimbrough with co-research by Anjali Kumar

Most “run-of-river” hydroelectric dams in the Amazon Basin are used to divert all of the flow away from the natural river channel to generate electricity in a powerhouse located downstream. Such dams disrupt ecological connectivity and eliminate any flow-dependent uses in the affected section of river. Photo credit: Ecuadorian Rivers Institute.

High in the Andes Mountains, countless minor streams begin their pilgrimage downward, joining forces with the rain to form the tributaries of the Amazon River. The sediments and organic matter they carry with them on their journey seaward are the nutrient-rich lifeblood that nurtures and sustains the vast aquatic and terrestrial web of life in the Amazon Basin.

This powerful downward flow of energy is increasingly being dammed to generate hydropower. Although the exact number of planned projects is in flux, 151 dams had been proposed for 5 of the 6 major Andean tributaries to the Amazon as of 2014 – a number that is bound to grow.

Unfortunately, poorly planned hydroelectric projects can open a Pandora’s box of environmental problems, including disruptions to free-flowing river connectivity, loss of biodiversity, deforestation, and fragmentation of ecosystems.

The seriousness of those hazards has not been thoroughly researched, but scientists interviewed by a team have expressed strong views regarding the dangers surrounding the proliferation of Andean-Amazon dams.

“I’m concerned about the fact that there are so many dams being proposed and constructed on Andean-Amazon rivers,” Dr. Elizabeth Anderson, the Director of International Research Programs at Florida International University told

“There have been dams in this region for many years – one example is the HidroAgoyan Dam in Ecuador which fragmented the Pastaza River, and has been in place for decades. So the fact that dams are being built is not new. What’s different about the current scenario is the sheer number of new projects, and the fact that many are quite large in size – larger than existing projects – and therefore are likely to have considerable ecological and social impacts.”

Roads to ruin


The first is the worst. New roads open up territories for development. Photo credit: Rhett Butler.
The first is the worst. New roads open up territories for development. Photo credit: Rhett Butler.

One of the biggest immediate environmental impacts will arise not from the proliferation of hydroelectric dams themselves, but from the road networks and electrical transmission lines that must be built to support dam construction and operation.

More than 80 percent of the proposed Andean Amazon dams will likely drive major deforestation due to new roads and flooding, according to a 2012 paper by Finer and Jenkins published in PLOS ONE.

“It is important to understand that a new hydroelectric project is more than just a dam structure,” explained Ecuadorian Rivers Institute Executive Director Matt Terry. “The development of new roads, gravel mines, logging [operations], work camps, and power transmission lines may cause additional environmental impacts, as well as the segregation and fragmentation of ecosystems and habitats. Later, these new accesses may become a driving factor for additional development and new settlement and intervention which amplifies the initial impacts to ecosystems.”

Dr. William Laurance of James Cook University supports that assessment: “There are over 150 large dams with greater than 2 megawatt capacity that are either planned or are under construction right now in the foothills of the Andes. There are 12 dams that are currently planned for the Tapajos River [Basin in Brazil] and it has been estimated that those 12 dams, because of the road networks, are going to result in almost 1 million hectares [3,861 square miles] of additional deforestation above and beyond the deforestation that would already happen. So, it is the opening up of these frontier areas that is the real problem.”

Shattering ecological connectivity


Finer and Jenkins 2012: Existing and planned Hydroelectric dams of the Andean Amazon. Dams sorted by status (existing and planned) and size (2–99 MW, 100–999 MW, and ≥1,000 MW capacity). doi:10.1371/journal.pone.0035126.g001 Map Credit: Finer and Jenkins / PLOS One.. Click image to enlarge.

The Amazon River and its basin are intimately linked to the Andes Mountains. Placing 151 dams on major tributaries will create the first major break in that connectivity in 10 million years – with largely unknown ecological consequences.

Each of the Andean Amazon tributaries is a unique system with unique diversity patterns. However, those rivers are part of a bigger, more complex pattern of ecosystem functioning. “Losing or damaging the connectivity between these systems and the main stem of the Amazon is like cutting veins or creating clots in a circulatory system,” Jorge Celi told Celi is a specialist who has studied aquatic ecosystems in the Napo River basin since 1992.

“Massive dam proliferation would dismember whole river systems and isolate biological populations with damaging and lasting impacts to the levels of diversity of the [Amazon] Basin, its functioning, and the services that it provides,” Celi stated. “It could create cascading [impacts] that could affect the most diverse ecosystem on earth with consequences to the whole planet and humanity.”

The Andes Amazon ¨white water streams¨ provide a broad range of ecological benefits. Numerous economically and ecologically important freshwater fish species migrate from the lowlands to the foothills to spawn.

The Andean tributaries also offer an annual supply of organic matter that supports the full range of tropical freshwater aquatic life throughout the Amazon Basin. The new dams, if built, will retain all of those sediments and nutrients and alter the flow of tributaries, with dire consequences for downstream productivity, floodplain sediment deposition, living organisms and people.

This Amazon river drainage flows freely from its source in the Andes. Photo credit: Ecuadorian Rivers Institute.This Amazon river drainage flows freely from its source in the Andes. Photo credit: Ecuadorian Rivers Institute.


A 2014 study published in Nature Geoscience found that Amazon River Basin lowland rivers that carry large volumes of sediment meander more across floodplains than rivers that carry less sediment. This potential for the “reshaping of the floodplain environment” and the limiting of the distribution of organic matter, say the scientists, has clear implications for the Amazonian river system. Lowland rivers and their floodplains would see significantly disrupted sediment loads if the proposed dams are built, and not spread nutrients as widely.

“Sediment retention and altered flow regime could also cause geomorphological destabilization of river banks and levees that local people depend on for living and farming sites,” explained Dr. Steve Hamilton, a Michigan State University scientist who studies the movement of water through landscapes. “In low gradient rivers the backwater effect of the dam can permanently flood large areas of river channel and floodplain habitat that formerly had a seasonal flood pulse.”

In their 2012 paper, Finer and Jenkins warn that: “Major breaks in connectivity could bring severe and unpredictable impacts.” The researchers looked at all 151 proposed dams, and found that 47 percent would have a high impact. “Sixty percent of the dams would cause the first major break in connectivity between protected Andean headwaters and the lowland Amazon,” the authors wrote.

“Although there is relatively very little known about the full extent of the ecological connections between the Andes and the Amazon, I think that it would be safe to say that Andes-to-Amazon connectivity provides the structural foundation for a contextual relationship from which nearly all of the [region’s] known biodiversity, habitats, and ecosystems have been derived,” said Matt Terry. “Simply put, without the emergence of the Andean cordillera and the processes which continue to shape its active formation, there would be no Amazon Basin as we know it.”

Unimaginable biodiversity crash?

The species most likely to be adversely impacted by the connectivity-breaking dams of the Andean Amazon will be migratory fish, aquatic plants and animals, and riparian and floodplain flora and fauna. Unfortunately, scientists know very little about the extent of the species that could be affected. This great lack of adequate scientific research and data for Andean-Amazonian aquatic species is a problem mentioned in nearly every interview.

These yellow lady-slipper orchids (Phragmipedium reticulatum) are an example of the native riparian vegetation found along Andean Amazon rivers, plants that are dependent on a natural flow regime to provide very specific conditions for moisture, temperature and humidity. Photo credit: Ecuadorian Rivers Institute
These yellow lady-slipper orchids (Phragmipedium reticulatum) are an example of the native riparian vegetation found along Andean Amazon rivers, plants that are dependent on a natural flow regime to provide very specific conditions for moisture, temperature and humidity. Photo credit: Ecuadorian Rivers Institute.

“To my knowledge, there is inchoate scientific understanding of the current hydrology of Andean/Amazonian streams. When we alter them by building dams, we affect the entire aquatic system,” commented Catherine Schloegel, Executive Director of Fundación Cordillera Tropical. “Certainly experiences in North America suggest that fish species – think of the pikeminnow in the upper Colorado River, for example – need both peak high/low flows, to reproduce. When we tame wild Andean rivers and create uniform flow [with a large dam], we [will] drastically alter the entire downstream ecosystem in ways that we can scarcely imagine at the onset.”

The Colorado pikeminnow (Ptychocheilus Lucius), which grew to six-foot lengths, was an abundant migratory fish and valuable food source for pioneers on the main stem of the Colorado River and its tributaries in seven states. The pikeminnow required uninterrupted river passage and a natural flow characterized by large spring snowmelt runoff and lower, stable base flows. Colorado River system dams made it an endangered species. Today, just two isolated wild populations remain.

The freshwater pink river dolphin (Inía geoffrensis). Photo credit: Georg Sanderadapted under a CC BY-NC 2.0 license.
The freshwater pink river dolphin (Inía geoffrensis). Photo credit: Georg Sander adapted under a CC BY-NC 2.0 license.

The freshwater pink river dolphin (Inía geoffrensis) could suffer a similar fate if the South American dams are built improperly. It is one of the Andean Amazon’s most iconic aquatic species and would be directly affected by connectivity-breaking dams. These dolphins live in the upper reaches of the Madeira River in Bolivia and in the Orinoco Basin. They move out of the main river channels into flooded forests during the rainy seasons. Data is lacking on dolphin numbers so their conservation status is not known. However, improperly placed dams could have a devastating impact to their habitats and food resources.

The Andean tributaries are incredibly biodiverse. Over 600 species of fish have been identified in the Napo River watershed alone, and new species are found on each sampling trip, making the Napo one of the most biodiverse rivers in the world in terms of fish species in relation to river size. The Napo River is one of the last remaining free-flowing major tributaries of the Amazon.

Amazon fish, Loricaridae. Photo credit: Sebastian Heilpern.
Amazon fish, Loricaridae. Photo credit: Sebastian Heilpern.

“The proposed Mazán hydroelectric project threatens to disrupt the ecological connectivity of the Napo River at the base of the entire watershed, just above the confluence with the Amazon,” reported Matt Terry.

The long-distance migratory catfish, representing the Pimelodidae family, and other migratory fishes in the Prochilodontidae family would also likely be affected by disruptions in river connectivity. Negative impacts to fisheries may affect the food supply and food sovereignty of local populations and indigenous communities who rely on subsistence fishing as an important source of protein throughout Amazonia.

Amazon fish Pimelodidae,
Amazon fish Pimelodidae, “Zungaro”, migratory catfish. Photo credit: Sebastian Heilpern.

The endangered Giant River Otter (Pteroneura brasiliensis), which has already lost 80 percent of its range in the Amazon Basin, is at risk from dams that would further degrade its habitat and impact the fish species that it relies upon for food.

German herpetologist Claudia Koch recently discovered 14 species of reptiles and amphibians new to science in the Marañón River Valley of the Peruvian Andes in just 13 months of research. The Marañón is considered the main source of the Amazon. Koenig worries that those animals, along with many as yet unidentified endemic species, will be “lost forever” if proposed dams are built there.

Innumerable rare and endemic plant species make a home in and along the Andean tributaries, and require the specific microclimates created by natural flow regimes to survive. “The aquatic plant species, Myriocolea irrorata, for example, grows only in a specific section of the Topo River in the Pastaza watershed of Ecuador and is threatened with extinction by the development of a small, 27 megawatt, run-of-river hydroelectric project [the Topo hydroelectric project] which has broken perhaps the most important free-flowing, Andean Amazon connectivity in the Pastaza watershed,” said Matt Terry.

Myriocolea irrorata, a liverwort endemic to the Topo River in the Pastaza watershed of Ecuador. Photo credit: Lou Jost.
Myriocolea irrorata, a liverwort endemic to the Topo River in the Pastaza watershed of Ecuador. Photo credit: Lou Jost.

Reservoir and atmospheric footprints

The impoundments created by large hydroelectric dams can flood huge areas and have massive footprints. The Balbina Dam in Brazil, for example, has flooded an area of about 2 million hectares (7,722 square miles).

The twenty hydroelectric dams planned for the 1,700-kilometer (1,056-mile) Marañón River would inundate approximately 7,000 square kilometers (2,703 square miles) along 80 percent of the river’s main trunk, according to a 2014 report by the US-based NGO International Rivers. “The currently vibrant and free-flowing river would be almost completely drowned,” said the report. More than 40 dams are slated for the Marañón’s main stem and its tributaries – and this is just one of the five major Andes Amazon tributaries where hydroelectric projects are proposed.

Dams inundate forests, habitat, farmlands and communities in the short term, but they also have long-term implications for global climate.

“When you destroy that forest and you flood it, the trees break down anaerobically and that turns their carbon into methane gas, one of the worst greenhouse gases,” Dr. William Laurance told “The other thing that tends to happen in these dams is that you have a large distinction between the wet and dry seasons, so the dams tend to draw down a lot in the dry season and fill back up in the wet season.” When tropical dams experience low water levels there is a great deal of rapid plant growth along the exposed shorelines. Then when the dam re-floods in the wet season that vegetation dies, rots and turns into more methane gas. Methane is roughly 20 times more powerful as a greenhouse gas as carbon dioxide.

“So there are a whole series of impacts that happen, both local and regional scale impacts, as well as global scale impacts, that results from [Neotropical] dams,” concluded Laurance.

A cataclysmic game changer

“Hydropower can be part of a sustainable energy future if designed and operated in a manner that avoids and minimizes impacts on vital river functions.” Jeff Opperman, Lead Scientist of The Nature Conservancy and of the Great Rivers Partnership Initiative told “A scenario of dams located high in the [Andes Amazon] watershed and only on some of the tributaries might have the least amount of impact on the environment and still provide significant electricity benefits. The degree of the impact is very much a function of good siting and design.”

One ideal strategy: build no dams on main stem Amazon tributaries, including the Marañon, Madeira, Napo, Putumayo and Ucayali rivers, and designate and protect these streams as “free-flowing” waterways.

Free-flowing Andes Amazon rivers are vital to aquatic and terrestrial species, and to indigenous peoples. Photo credit: Ecuadorian Rivers Institute.
Free-flowing Andes Amazon rivers are vital to aquatic and terrestrial species, and to indigenous peoples. Photo credit: Ecuadorian Rivers Institute.

Unfortunately, there is currently no basin-wide authority to coordinate hydroelectric projects, though some are pressuring the Amazon Cooperation Treaty Organization (OTCA) to take on the task. Regardless, there is an urgent need for research, holistic planning, funding, policy mechanisms and incentives if the free-flowing health and vitality of the Andean Amazon tributaries are to be maintained.

“The Amazon dams are going to be a game changer for the Amazon, unfortunately,” concluded William Laurance. “I think they are an environmental disaster wrapped in a catastrophe, the way that they are currently being developed and proposed. I am very, very concerned.”





Exit mobile version