Frequently Asked Questions

Q: Why are healthy rivers important?

Healthy rivers are the lifelines of our planet, and provide many critical services for free. Rivers and their watersheds – and the rich variety of plants and animals which they sustain – provide people with water for drinking, watering crops, and washing, and with food, medicines, building materials, and more. They also filter out pollutants, mitigate floods and droughts, recharge groundwater supplies, and sustain fisheries. Rivers are also important byways for travel.

A river is much more than flowing water. Its ever-shifting bed and banks, the groundwater below, its surrounding forests, marshes and floodplain are all parts of the river. A river carries not just water, but just as importantly nutrient-rich sediments and dissolved minerals that replenish the land.

The river’s estuary, where fresh water mixes with the ocean’s salt, is one of the most biologically productive parts of the river – and of the planet. Most of the world’s fish catch comes from species that depend for at least part of their life cycle on estuarine habitat.

Q: How do large dams affect rivers and the environment?

The damming of great rivers is among the most dramatic, deliberate impacts that humans have on their natural environment. Nothing alters a river as totally as a dam.

A dam is an attempt to bring a river under control, to regulate its seasonal pattern of floods and low flows. A dam traps sediments and nutrients, alters the river’s temperature and chemistry, and upsets the geological processes of erosion and deposition through which the river sculpts the surrounding land. Such changes can throw an entire watershed out of ecological balance.

More than 45,000 large dams now block most big river systems. Dams now hold back 15% of the world’s annual freshwater runoff. If we want to sustain the world’s biodiversity and riverine goods and services, then we need to replace large dam building with alternate solutions.

• Read more about the Environmental Impacts of Dams.

Q: How do large dams affect people?

An estimated 40 to 80 million people have been displaced by dams. At present perhaps two million people are displaced every year by large dams. Many times more people also suffer from the downstream impacts of dams, which can include loss of fisheries, decreased water quality and a decline in the fertility of farmlands and forests due to the loss of natural fertilizers and seasonal floods that healthy rivers provide.

In nearly every case, the majority of people evicted by dams end up further impoverished, and rarely share in project benefits. They suffer cultural decline, high rates of sickness and great psychological stress. The ones who suffer are typically those most marginalized in society – poor farmers and indigenous people. In some cases, people receive no or negligible compensation for their losses. Where compensation is given, cash payments are rarely enough to compensate for the loss of land, homes, jobs and businesses. Dam-affected communities are often promised great improvements such as electricity, new clinics and improved schools. Such promises are often broken.

For a visual introduction to dams, rivers and people watch our We All Live Downstream slideshow, and watch the below short film, A River Runs Through Us.

Q: But aren’t dams a source of clean energy?

Dams are not “clean” sources of electricity because of their serious social and environmental impacts. In addition, studies reveal that rotting organic matter in dam reservoirs produce greenhouse gases. In some cases, especially in the tropics, reservoirs can produce more greenhouse gases than even the dirtiest fossil fuel power plants. The Balbina Dam in the Brazilian Amazon is estimated to produce 20–40 times the amount of carbon dioxide produced by coal fired power plants.

• Read "Greenwashing Hydropower": The Problems with Big Dams.

Q: Don’t dams produce cheap electricity?

Economically speaking, hydroelectricity is cheap to produce – once the dams are built. The problem is the huge costs of building dams and the long time it takes to build them. Actual costs for hydropower dams are almost always far higher than estimated; in a number of cases, the actual cost was more than double the estimated cost. The Itaipu Dam in South America cost $20 billion and took 18 years to build. This was 488% higher than originally estimated.

Dams often produce less power than promised – and as climate change is expected to change river hydrology in many parts of the globe, power output from dams could become even more unreliable. Dam promoters do not take into account the risk of climate change impacting their projects, which adds to the already optimistic cost-benefit estimates that characterize so many dam projects. In addition, the transmission lines needed to distribute the power generated by the dam are often inefficient and expensive. Too often in many poor countries where large dams are being built, electricity grid coverage is very limited, and the cost of extending the grid from a remote dam to where the need is greatest is not included in project costs. When these factors are taken into account, hydropower is actually a very costly form of power generation.

Q: What forms of power generation do large dam critics support?

No energy source is a “silver bullet” for meeting the world’s growing energy needs. The key is to openly assess energy needs against the various options for meeting that need, while also being honest about the costs and benefits (and the distribution of these costs and benefits) that various project options would bring. Energy needs must also be balanced against other societal goods, such as those provided by healthy rivers.

One of the first "sources" of energy we should look to is energy efficiency. Electricity use in most parts of the world is extremely wasteful. The priority before building new power plants should always be to improve the efficiency of existing energy supply and use. Energy losses through inefficient systems can be huge even in developing countries with low production of electricity. As an example, almost 50% of power generated in India is lost before reaching the consumer. Indian energy analysts have estimated that improved efficiency could provide the entire increase in energy supply supposed to be needed over the next decade, at a fraction of the cost of new supply.

When new power plants are clearly needed, prioritizing the use of decentralized renewable energy solutions such as wind, solar, geothermal (and perhaps in future, wave power and other technologies) has many advantages. Small dams can be a sustainable and economic source of electricity, especially in rural areas – as long as they are designed to protect basic river functions such as fish migration and sediment flow. All of these options can help bring electricity to the parts of the world that need it most: rural communities far from national electricity grids.

Q: How can we reduce poverty in developing countries unless we exploit all available power sources, including hydro?

Like other investments, funding for the power sector in developing countries is limited. Better processes for selecting energy projects can help avoid the political favoritism (and even bribery) that now often influences the decision-making process, and too often leads to white-elephant dams being built.

The World Commission on Dams, an international panel that provided the first independent and comprehensive assessment of dams, devised an approach to dam-planning in which affected communities negotiate their own compensation packages, and become primary beneficiaries of dam projects’ benefits. Dams planned using the commission’s recommendations and guidelines are more likely to go forward only after carefully analyzing all available options, and through a fair and transparent planning process. A few countries – for example, South Africa – have taken steps to incorporate the WCD’s recommendations into their planning processes for water and energy projects.

Q: What about the jobs produced by dams?

In developing countries (where most dams are being built today), most jobs to design and build dams go to highly trained engineers and contractors who are brought in to build the project, not local people or even citizens of that country. Maintaining dams provides fewer jobs, so the long–term jobs benefit is often minimal. Wind power creates 4–10 times more jobs per unit of output than large hydro (and biomass and solar power can create many more jobs than wind).

Q: Are dams an effective method of stopping flood damage?

When a dam is built for flood control and other uses, the floodplain no longer serves the ecological function it once did for the community, and more people move into the most flood–prone lands, believing they will be protected from all floods. The dam reduces the frequency of floods, but does not prevent the biggest, most damaging floods from occurring. The result: more expensive damages from floods than ever before. A "soft path" to flood management would better prepare us to adapt to and work with the forces of nature

Q: What about water storage – surely, we need dams for that?

Water storage is a critical need in all parts of the world, and of growing concern due to population growth and climate change. There are many ways to improve not only how we store water, but also how we conserve it.

Better solutions tend to work with nature, rather than against it, and make effective use of "ecosystem services" provided by healthy watersheds and other ecological systems. And by relying on better technologies and more informed choices, these solutions seek to raise water productivity.

Working with nature is critically important to building resilience and reducing the energy costs associated with water delivery and use. Healthy rivers and watersheds, for instance, filter out pollutants, mitigate floods and droughts, recharge groundwater supplies, and sustain fisheries. By contrast, all the technological alternatives – building and running a treatment plant to remove pollutants, artificially recharging groundwater, constructing dikes and levees, raising fish on farms – require external inputs of increasingly expensive energy.

• Read “Adapting to a New Normal” by water expert Sandra Postel.

Q: Are dams a safety concern?

The global stock of dams as a whole is aging, and as dams get old they become increasingly more expensive to maintain. Around the world, 5,000 large dams are at least 50 years old; the average US dam is in its forties. Worldwide, there is systematic underfunding of dam maintenance. It would cost billions of dollars to bring the world’s dams to safety. In addition, there is increasing concern that dams can trigger earthquakes from the weight of the reservoir, among other factors. Earthquakes also increase the probability of dam failure and the risk of downstream flooding.

Today, the biggest dam–safety challenge is climate change. The world’s more than 45,000 existing large dams have not been built to allow for a rapidly intensifying hydrological cycle. In this sense, all dams should now be considered unsafe. While the climatic future is filled with uncertainties, climatologists almost universally agree that we will see (and indeed are already seeing) more extreme storms and increasingly severe floods – which will have major implications for dam safety.

Q: What is “dam decommissioning”?

The United States, whose 5,500 large dams make it one of the most dammed countries in the world, has stopped building large dams, and is now spending great amounts of money trying to fix the problems created by existing dams. Many US communities are revitalizing their rivers by taking down or otherwise “decommissioning” dams that are no longer safe or serving a justifiable purpose. Over the past decade hundreds of dams have been removed from US rivers, opening up habitat for fisheries, restoring healthier water flows, improving water quality, and returning aquatic life to rivers.

Q: Do critics of large dams oppose all dams?

In general, no. They do believe that dams (and other development projects) should only be built after all relevant project information has been made public; the claims of project promoters of the economic, environmental and social benefits and costs of projects are verified by independent experts; and only if affected people agree that the project should be built.