In recent decades, humans have built many dams. These are designed to regulate flow for irrigation, hydropower and water supply. Most major rivers in the world are dammed.
But there are detriments to damming rivers. Many people depend on the natural ebb and flow of unrestricted rivers that swell with water in the rainy season and wane in the dry season. When the natural flow is changed, people and ecosystems are affected: globally, an estimated 472 million people living downstream of dams have suffered adverse effects from changes to the rivers’ flows.