Final answer:
An estuary is a wide area at the mouth of a river where it meets the sea, and in a reverse estuary, surface water flows out to the ocean while bottom water moves toward the river.
Step-by-step explanation:
An estuary is a wide area at the mouth of a river where it meets the sea. In this type of estuary, known as a reverse estuary, the surface water flows out to the ocean, while the bottom water moves toward the river. This creates a unique flow pattern that allows for the mixing of fresh and salt water.