At first glance, hydroelectric dams seem like a relatively benign source of renewable energy. They don’t churn out dangerous plumes of smog or house radioactive materials that threaten to turn whole regions into uninhabitable wastelands. They don’t inject poisonous chemicals into the water table, and besides, it’s water, so it must be clean, right?

For the better part of the last century, dams have been heralded as modern day wonders of engineering. They exemplify mankind’s ability to harness the natural world, and are sources of national pride and a signature of a country’s progress. While it is true that these dams are technological marvels and an efficient way to produce energy, that is only half of the story. While dams may not have the reputation for failing in the sudden and catastrophic ways that nuclear reactors or offshore oil rigs do, they can and do often have similar catastrophic consequences.


According to International Rivers, there are over 40,000 large dams dotting rivers all over the globe. Upstream from each of these is a floodplain or reservoir, where the bottlenecked river pours across the surrounding lands. Depending on the size of the dam, that area can be massive. In some cases, the size and scope of the flooding can mimic a natural disaster; the floodplain of China’s Three Gorges Dam, for instance, was so large that it displaced an estimated 1.5 million people. The World Commission on Dams estimates that the number of people displaced by hydroelectric dams worldwide falls somewhere between 40-80 million.

These numbers are truly astonishing, but they still say nothing of the ill effects visited on communities living downstream. The ecological damage that dams can cause are well documented, and communities that depend on rivers for fishing and agriculture often find themselves out of luck. Fish populations ­suffer severe declines and lands become less productive as nutrient rich sediment delivered by the river becomes scarce.  For those that do not depend on fishing or farming for their own personal survival this may not seem like a big deal. However, in regions of the world where vast numbers of people depend on these methods as their sole source of food and income, dams can have widespread negative impacts on food security and local economies.

Children fishing in the Mekong River in Cambodia

For instance, the lower Mekong River, one of the largest and most ecologically diverse rivers on the planet, directly provides food to over 60 million people. Currently, the Xayaburi Dam (under construction) and the proposed Dah Sahong dam are moving forward in Laos, and up to 21 dams are planned in the Chinese section of the Mekong River despite widespread protests from downstream countries where the lives and livelihoods of millions are in jeopardy.  Rotting plant material in the reservoir of the Nam Theun 2 dam in Laos, financed by the World Bank, is responsible for the emission of as much as one million tons of methane and carbon dioxide per year. This is 40% of the Green House Gases (GHG) that would be emitted from a coal fired power plant of equivalent energy output, and far more than a natural gas-fired plant. (For more on the Mekong River and the ecological impacts of proposed dams, this Ted Talk by Stuart Chapman of the World Wildlife Fund is a great place to start and International Rivers’s report on GHG emissions of dams).

When we see the sheer scale of the negative impacts dams can have, we have to ask ourselves, who do they serve and how much are we willing to trade for the energy that they produce?

In the Cajamarca region of Peru, local communities are asking just that. On the banks of the Marañon River (one of the Amazon River’s main tributaries), indigenous communities are worried that the Chadin II dam—one of Peru’s 24 planned hydropower projects along the same river—will flood their villages and leave them without a way to support themselves. There are additional concerns that the dam is being pushed forward not because of the energy demands of Peruvian citizens, but because of the nearby Conga Mine—itself the subject of community protests and subsequent violent crackdowns by police. The belief is that the mine will not remain economically viable without  the local source of cheap energy that the dam can provide.

Indigenous communities in the Cajamarca region of Peru fight the proposed Chadin II dam on the Marañon River

Thankfully, the growing understanding of dams’ negative impacts and the increasing number of grassroots campaigns resisting their development has slowed the zeal with which hydroelectric projects are being pursued. Now, a new study disputing the economic feasibility of these projects may finally mark the beginning of the end for the era of the mega-dam.

The peer-reviewed study, conducted by researchers at Oxford University, catalogued the available records for all large dams built between 1937 and 2007. They found that on average, large dams run over budget by 96%, and that the predicted timetables for construction were exceeded by 44%. According to the researchers, these routine overages, if reflected realistically during the planning stages, would make a number of proposed hydropower projects economically infeasible.

The money spent on each mega-dam, like the Three Gorges, can reach into the tens of billions of dollars. The engineers working on these projects are among the most brilliant in the world. Still, we stubbornly push forward with an outdated model whose human and environmental impacts are disastrous, and whose economic feasibility is now being called into question. Hydro-power can and should be a part of the global strategy to meet our collective energy needs, but it is time for the financiers of large-dams to begin funneling the minds and money at their disposal into developing new models. If our collective will and resources are put in the right places, development, displacement, and environmental degradation do not have to go hand in hand. With all those resources, they can do better

Let us remember the human and environmental impacts of hydroelectric dams on World Rivers Day, and every day.