A delta is a landform shaped like a triangle that is created by the deposition of sediment carried by a river and entering slower-moving or stagnant water. Deltas are wetlands that form as rivers empty their water and sediment into another body of water, such as an ocean, lake, or another river. Deltas have a rich accumulation of silt, so they are usually fertile agricultural areas. The worlds largest delta is the Ganges-Brahmaputra delta in India and Bangladesh, which empties into the Bay of Bengal.
Deltas have been important in human history. Historians believe that it was in a fertile river delta in Mesopotamia where humans first learned to harness the power of water for irrigation in agriculture. Today, deltas are often ideal places for civilization and are home to many people and a lot of the world's agricultural production.
There are different types of deltas, such as river-dominated deltas and tidal-dominated deltas, depending on the influence of waves, tides, and river flow. Human activities in both deltas and the river basins upstream of deltas can radically alter delta environments. Upstream land use change such as anti-erosion agricultural practices and hydrological engineering such as dam construction in the basins feeding deltas have reduced river sediment delivery to many deltas in recent decades. Urban areas and human habitation tend to locate in lowlands near water access for transportation and sanitation, making deltas a common location for human activities.
