What is the prepositional phrase for sentence Water flowed under covered bridge.?

The prepositional phrase in the sentence "Water flowed under the covered bridge." is "under the covered bridge".

Here's why:

* Preposition: "under"

* Object of the preposition: "the covered bridge"

The prepositional phrase acts as an adverbial phrase, modifying the verb "flowed" by telling us where the water flowed.