A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity.
A dam can also be used to collect water or for storage of water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions.
Here are the top 20 largest dams in the world.
| Rank | Name | Country | Structure volume |
| 1. | Tarbela Dam | Pakistan | 153 million m3 |
| 2. | Fort Peck Dam | United States | 96 million m3 |
| 3. | Atatürk Dam | Turkey | 84.5 million m3 |
| 4. | Houtribdijk | Netherlands | 78 million m3 |
| 5. | Oahe Dam | United States | 70.3 million m3 |
| 6. | Mangla Dam | Pakistan | 65.4 million m3 |
| 7. | Gardiner Dam | Canada | 65.4 million m3 |
| 8. | Oroville Dam | United States | 59.6 million m3 |
| 9. | San Luis Dam (BF Sisk Dam) | United States | 59.6 million m3 |
| 10. | Nurek Dam | Tajikistan | 54 million m3 |
| 11. | Samara Dam | Russia | 54 million m3 |
| 12. | Garrison Dam | United States | 50.8 million m3 |
| 13. | Cochiti Dam | United States | 50.2 million m3 |
| 14. | Aswan Dam | Egypt | 44.3 million m3 |
| 15. | W. A. C. Bennett Dam | Canada | 43.7 million m3 |
| 16. | San Roque Dam | Philippines | 40 million m3 |
| 17. | Fort Randall Dam | United States | 38.2 million m3 |
| 18. | Afsluitdijk | Netherlands | 36.5 million m3 |
| 19. | Kölnbrein Dam | Austria | 35.2 million m3 |
| 20. | Guri Dam | Venezuela | 29.8 million m3 |
