When a river enters a **delta**, it typically slows down and spreads out as it approaches an **ocean** or a **sea**. This transition leads to the deposition of sediment carried by the river, creating rich, fertile land that forms various **landforms** such as islands and marshes. Deltas are vital ecosystems that support diverse wildlife and plant life. They also play an essential role in human agriculture and habitation due to their fertile soils. Famous examples include the **Nile Delta** in Egypt and the **Mississippi River Delta** in the United States.