An estuary in Texas gets cut off from the sea by the accumulation of sediment and sand at the mouth of the river. What type of geological feature has been formed?

The blocking off of an estuary from the sea forms a (n)

lagoon

Explanation:

As the estuary gets more and more sediments, the deposition of them is constantly on the rise, affecting the landscape and forming new geographical features. With the sediments constantly building up, they eventually cut off part of the water from the sea. They will form a closed pool-like feature, filled with water, and surrounded by sediments, cut off from the sea. It will have shallow water, and because the water is stagnant and shallow it will have higher temperature than the other water. This geographical feature is known as lagoon.