Final answer:
Salt-wedge estuaries have sharp boundaries between fresh water and salt water.
Step-by-step explanation:
Salt-wedge estuaries have sharp boundaries between fresh water and salt water. Estuaries are biomes where a source of fresh water, like a river, meets the ocean. In these areas, the mixing of fresh water and salt water creates a zone where the two types of water have distinct boundaries. These boundaries can be sharp, meaning that there is a clear separation between the fresh water and salt water in the estuary.