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Hesperian Health Guides

Large Dams Damage Health

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HealthWiki > A Community Guide to Environmental Health > Chapter 9: Protecting Watersheds > Large Dams Damage Health

A dam is a wall built across a river. Dams are built to block the flow of a river and form a human-made lake called a reservoir. Water stored in reservoirs can be used to control flooding, to provide water for irrigation and drinking, to make electricity, or for recreation.

Dams have contributed to building modern cities and improving many lives. But large dams, more than 15 meters tall and sometimes as tall as 250 meters, also harm people and the land in many ways.


How a large dam made the Yaqui people sick
A man standing beside a dam.

Many years ago the Yaqui people lived by farming in the hot, dry climate of northern Mexico. Thanks to their river, the Rio Yaqui, they had water for farming, for drinking, and to meet their needs all year.

This all changed when their river was dammed. The Mexican government agreed that half of the water from the dam belonged to the Yaquis. But the Yaquis soon found that no water arrived at their villages. The entire river had been channeled into a giant canal to irrigate many large industrial farms growing wheat and cotton. These large farms soon surrounded the Yaqui villages, and the Yaqui people were left with no water for their own crops.

To grow wheat and cotton in dry desert soil requires a lot of water, chemical fertilizers, and pesticides. Pesticides are sprayed as many as 45 times in the months between planting and harvest. All of this poison ends up in the irrigation canals. With their river diverted and no other source of water, the Yaquis drink from the canals. Over the years, the polluted water made them sick.

After years of drinking contaminated water, Yaqui children were having problems learning, thinking, growing, and playing. Many children also suffered from severe health problems such as cancer of the blood and birth defects, such as withered limbs and soft bones. These health problems are most likely caused by drinking water and breathing air poisoned with pesticides.

The Yaqui people's health problems began when their river was dammed.

Dams cause problems upstream and downstream

First, dams create problems for people who live upstream from where the river is or will be blocked.

Displacement and poverty

People are displaced by dams and forced to migrate. Many end up living on poor land or in urban slums. Displaced people may be promised money or land. But often money is not handed over by local officials. Many times, only people with legal title to land that will be flooded by the dam receive money or other land. Sometimes, the replacement land is too poor to farm.

Towns that will be flooded by a dam do not receive government funds for upkeep and development, so schools, roads, and health services fall into neglect. Some towns remain like this for many years before they are flooded.

Dams destroy the natural flow of the river. They cause either an increase or decrease in water flow, depending on the dam. The natural cycle of flood and drought may be disrupted, affecting the entire river and damaging huge areas of land.

New insect breeding grounds

Mosquitoes breed in the shallow, sunny waters of irrigation canals, and at the edges of reservoirs. Regularly raising and lowering the level of the reservoir can kill young mosquitoes. But the people who manage dams do not usually consider this important.

Black flies that spread river blindness lay their eggs in fast flowing water, like the water that flows out of a dam. The still waters in dam and irrigation projects are breeding grounds for snails that carry blood flukes.

Erosion of riverbanks and floodplains

When a dam blocks a river, bits of soil and rock carried by the water (silt) settle on the river bottom and in the reservoir instead of on riverbanks. When water is let out of the reservoir, the water has no silt in it. Because silt is part of what makes land rich for farming, downstream lands become poor. And because water released from the dam collects silt as it moves, it further erodes the land as it digs deeper into the riverbed.

A dam creates a reservoir with a village beside it and a flooded village in it.
Dams builders are oppressed. They often have unsafe work conditions, poor housing, bad food, and little access to health care. These conditions promote illnesses such as TB and HIV. After a dam is built, they must find another place to live and work.
Dams destroy communities. Families living in the reservoir area lose their homes, lands, and livelihoods. Displaced people are often not resettled together. People are usually poorer after they move.
Reservoirs are often polluted. Pesticides, fertilizers, and industrial waste may collect in the water, making it toxic.
Reservoirs create other health problems. Diseases such as malaria and blood flukes increase when reservoirs breed mosquitoes and other disease-carrying insects.
Dams kill fish and destroy fisheries. Changes in the flow and quality of rivers can destroy fish. People who depend on fish for food and income suffer.

Electric wires and a pipeline go from a village to a city.
Dams take water from rural communities. Water once used by rural farmers and people who fish is used instead to generate electricity for cities and industry.
Crop yields decline. Dams flood productive farmlands and block silt from flowing downstream to fertilize crops. Water released from dams can wash out riverbank gardens.
Dams release polluted water. Poor quality water causes illnesses for people and animals downstream.

Alternatives to large dams

A prone man reaches for a glass of water; on his back are stacked 3 large sacks labelled "Flood control, Electricity,"and "Irrigation." Beside him are the words "for someone else."
But where is my water?

When there are plans to build a dam, the first question to ask is: Is it necessary? Dams are built for flood control, electricity, irrigation, and to provide water to growing cities. These services could be provided in less harmful ways.

The second question to ask is: Who is going to benefit? Around the world, communities that would be harmed have resisted big dams and proposed alternatives. In many cases, they are succeeding.

Flood control. If possible, avoid building in natural floodplains and wetlands. Improve warning systems to help people prepare for floods. Preserving the natural flow of rivers can prevent floods more effectively than damming them.

Electricity. Encourage governments and developers to promote wind, solar, or small-scale water power that generates electricity close to where it will be used. Locally managed and controlled energy is more sustainable for people in cities and towns, as well as in rural areas.

Irrigation. Local development provides better water security than large dams. In the state of Gujarat in India, thousands of small check dams have been built to collect rainwater for use in the dry season and to replenish the groundwater. The government and villagers share the cost of the check dams. Many villages that once had water to irrigate fields for only half the year, now have water all year round.

If a dam is proposed or built in your watershed

A long parade of people march across a river carrying signs which read "Water for People, Not for Profit," "We Won't Move,""It's Our Land," "No Dams," and showing fish skeletons.

Communities worldwide have been resisting new dams, working to have old ones taken down, and demanding compensation in both money and land for harm they have suffered from dams. Some communities also demand changes in the ways dams are controlled, to help rivers flow more naturally and reduce the harm dams have caused. (For more information, see Other Environmental Health Resources and Other Water and Sanitation Resources.)

Intertribal partnership protects the Yukon River

In Alaska and the Yukon Territory at the border of the United States and Canada, the mighty Yukon River flows 2300 miles (3700 kilometers) through many towns and villages. Because the river is threatened by contamination, 60 indigenous communities signed a treaty agreeing to work as partners to keep the river clean for future generations. They formed an alliance called the Yukon River Intertribal Watershed Council.

The Watershed Council did not begin by trying to clean up the entire river. They started with small projects and clear goals. One of their first programs was to ban the use of plastic bags in towns along the river. By banning plastic bags, people along the river learned that taking personal responsibility could make a big difference in protecting the watershed.

A group of villagers are smiling as they watch an elder sign a treaty.

After the plastic bag ban succeeded, the communities began cleaning up discarded batteries, oil, and broken down cars. Every community in the watershed built a landfill and set up a bin to collect batteries, keeping poisons out of the soil and water. Then they worked to convince all the small airlines, shipping companies, and military bases in the area to dispose of old batteries, cars, and oil safely.

Now, Yukon tribal governments are improving their sewage systems and landfills, and creating programs to recycle and reuse trash. They teach young people to test the water for pollution and to recognize signs of contamination in order to prevent it.

The Yukon River Intertribal Watershed Council built partnerships with tribal, state, local, and national governments in Canada and the United States, and with environmental and watershed groups, funding agencies, and outside advisers. By bringing many groups together, the Watershed Council was able to make a plan that included everyone in the watershed, and to gather enough resources to get the work done.

By taking small steps at first and then larger steps, the Watershed Council encourages change that is slow, but effective. One member of the Council said, “When I was a child I drank water straight from the river. In 50 years we will be able to drink from the river again.”

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