River-mouth regions, also known as deltas (6 letters), are areas where a river meets the sea or ocean. They are typically characterized by their flat, low-lying topography and are often rich in biodiversity due to the variety of habitats they provide. Deltas are formed when sediment is deposited at the mouth of a river, creating a fan-like shape. They are important ecosystems that provide many benefits to humans, such as providing food, water, and protection from flooding.