Unktehi was shaped like a giant scaly snake with feet. She had a huge horn coming out of the top of her head, and she filled
the whole of the Missouri River from end to end. The little water monsters, who lived in smaller streams and lakes, likewise had no use for humans.

"What are these tiny, lice-like creatures crawling all over the place?" they asked. "What are these blood-clot people creeping out of the red pipestone? We don't want them around!"

The Great Unktehi could place her body and puff it up in such a way that it made the great Missouri overflow, and her children, the little water monsters, did the same with their streams and lakes. So they caused a great flood that spread over the whole country, killing most of the people.

American Indian Myths and Legends, p. 220