What is the importance of the Mississippi River in the collection, American Indian Mythology?

The Mississippi River, like many other naturally occurring phenomena (mountains, lakes, plains, the sky, etc) was/is the focus of a number of mythic stories. These stories often told of how these phenomena came to be, but the story in this collection featuring the Mississippi River ("The Great River Monster, Part 1 Section 3) takes a slightly different tack as it tells why the river has the character it does.