The most significant characteristic of a delta is its sediment deposition at the mouth of a river where it meets a body of water, such as an ocean or a lake. This deposition occurs because the river slows down and loses its capacity to transport sediments, which accumulate to form the delta. Deltas are vital ecosystems, often rich in biodiversity and providing critical habitats for numerous species. They also play a significant role in agriculture, as their fertile soils are ideal for farming. Examples include the Nile Delta and the Mississippi Delta.