How is triangular area of soil at the mouth of a river?

The triangular area of soil at the mouth of a river, known as a delta, forms from the sediment deposited as the river slows and spreads out upon entering a larger body of water, such as an ocean or lake. The river's current loses energy, causing particles to settle and accumulate over time, creating a fan-shaped landform. Deltas are rich in nutrients and support diverse ecosystems, making them important for agriculture and wildlife. The shape and size of a delta can vary significantly based on sediment supply, water flow, and tidal influences.