This map shows dams and reservoirs around the world by their primary purpose. A dam is a structure constructed across waterways to retain water in a reservoir, or man-made lake. Dams are a tool used by humans to harness the power of water for millennia. Specifically, the map shows dams for hydroelectricity, irrigation, water supply, flood control, recreation, navigation, pollution control, fisheries and other non-specified uses. Some dams are multipurpose, meaning that they are used for more than one of these uses.

While the map does have global data, the most specific information is visible for the U.S. The legend labels the various symbols that represent the primary functions of global dams and reservoirs. Some rivers have a long history of flooding neighboring communities. Dams can control the water by releasing it gradually. Dams can generate hydroelectricity when the water flowing from a reservoir or river is used to turn turbines, thus creating energy. Farmers also use dams for irrigation methods. These dams divert water from a river or reservoir to bring much-needed water to crops that might not receive enough rain to grow properly. Dams can also manage water pollution through a variety of techniques, even trapping sediments and pollutants.

Water is important to our communities in many ways. Many reservoirs become lakes that bring hikers, boaters and fishing enthusiasts. Often a single dam will be used for multiple purposes. Lake Las Vegas and Lake Mead, managed by the Hoover Dam in Nevada, is a fitting example of a multipurpose reservoir. It provides water for consumption, generates hydroelectricity and facilitates recreation with boating, fishing and hiking trails.

Dams also have environmental consequences. They change natural systems. A blocked river can prevent natural fish migration patterns that impact species populations. Dams also slow the flow speeds of the water, impacting species that get their cues from season flow changes. The slower-flowing streams can decrease water quality. Dams change water temperatures by releasing flows of water from different levels of the reservoir, which have different temperatures. Warming water temperature can lead to algal blooms and oxygen-depleted waters. Dams also change habitats by creating ponds or reservoirs and drowning land upstream. Often, the land taken for the reservoirs is culturally significant to the Indigenous peoples who it originally belonged to. Rivers often cross political boundaries and provide water for people in multiple regions. A dam upstream in one country can negatively impact communities downriver, who may have less water for commerce, irrigation and food.

Global Dam Watch, an international collaboration organization, curates this data to improve understanding of costs and benefits of dams to our world. Their goal is to maintain the world’s most comprehensive and freely available global dam and data tools. Existing data are compiled, cleaned and curated. According to their site, new data are being collected using a variety of innovative methods from citizen science to remote sensing and machine learning.

Explorer Wangechi Kiongo - Environmental Conservationist and Community Champion

Lake Turkana in Kenya and Ethiopia is a unique ecosystem because it is the largest permanent desert lake in the world. The water has an unusual chemistry with high salt content and a distinct turquoise color. The three national parks near it are part of migrant birds’ journeys and are popular breeding grounds for the Nile crocodile, hippopotamus, fish and a variety of venomous snakes. Approximately 300,000 people also rely on the lake and its waters for their livelihoods. They use the lake for fishing, irrigation and drinking water for families or livestock.

Construction of a hydroelectric dam on the Omo River in the 2010s was set to dramatically alter the flow and health of water into the lake. National Geographic Explorer Wangechi Kiongo is a conservationist and environmental organizer from Kenya. Kiongo wanted to know how the dam could change the life of communities around Lake Turkana and how people and the environment could adapt to the changes the dam would bring.

Kiongo co-founded the Save Lake Turkana Movement, a youth-driven, voluntary, community-based organization. The movement's mission is to raise awareness about the importance of sustainability and to protect Lake Turkana, which is recognized as a UNESCO World Heritage Site. She worked with National Geographic to meet with people living around the Lake to discover ways to prevent both loss of local populations’ livelihoods and the loss of this world heritage site through overexploitation.

Thinking Geographically

Scale matters when exploring map data. As the map scale zooms out into space, the symbols begin to group or cluster and have a number in the center. That tells us how many items are located near that symbol. It’s easier to see from that view. Zoom closer to the ground, the individual dams and reservoirs appear with their primary purpose symbols and without numbers.

Search for Lake Turkana in Kenya, Africa. Pan and zoom the map to explore north of the Lake to find the “Gilgel Gibe III” dam. Click on the dam’s icon. What can we learn about power production in this area?

Zoom out to view the entire continent of Africa and North America in the same view. Which regions have the most dams? What areas have the most recreational use dams and reservoirs? Why might we know more about the purpose of dams and reservoirs in the U.S.?

Dig deeper into the data. Zoom into two or three different countries and select some of the dams in those countries. Be sure to scroll down to read the entire popup window and learn more about the number of dams and reservoirs as well as the power usage in each country. What stories do they tell us about water and power? How is your community affected by these resources nearby?