MG+shoals

http://thesaurus.reference.com/browse/shoals

The word shoals is not very common, and the writer uses it to create this world. The very world that this poem takes place in, the world that must be described through this word because it expresses the variety and difference.

How does a sandbar or one of the other definitions fit in here? Be sure to give your explanation enough detail so that our understanding of the poem is richer.