What is the term for a bay that becomes isolated from the ocean by sand deposits?

The correct term for a bay that becomes isolated from the ocean by sand deposits is a lagoon. A lagoon is typically a shallow body of water separated from a larger body of water, such as the ocean, by a barrier, which is often formed by sandbars or similar geological features. These barriers create conditions that allow for a distinct ecosystem to develop within the lagoon, influencing both the water's salinity and its biological diversity.

Understanding the contexts of the other options helps clarify why lagoon is the right choice. An estuary, for example, is where freshwater from rivers meets and mixes with saltwater from the ocean, creating a unique and productive environment, but it remains open to the ocean rather than being isolated. A delta forms at the mouth of a river where sediment is deposited as the river enters standing water, typically forming distributary channels rather than isolating a bay. An inlet, on the other hand, is a waterway that allows ocean water to flow into a bay or lagoon, maintaining a connection to the ocean rather than creating a separation. Thus, a lagoon most accurately describes a scenario where sand deposits isolate a bay from the ocean, encapsulating a distinct environment apart from those formed by the other options.