A Battle between the Thunderbirds and the Great Water Serpents as witnessed by the Lakota Sioux:
“Some of these ancient people still dwell in the clouds. They have large curved beaks, resembling bison humps, their voices are loud, they do not open their eyes wide except when they make lightning, and they have wings. They can kill various mysterious beings, as well as human beings. Their ancient foes were the giant rattlesnakes, and the Un-kche-ghi-la, or water monsters, whose bones are now found in the bluffs of Nebraska and Dakota. Long ago, the Tetons encamped by a deep lake, whose shore was inclosed by very high cliffs. They noticed that at night, even when there was no breeze, the water in the middle of the lake was constantly roaring. When one gazed in that direction he saw a huge eye as bright as the sun, which caused him to vomit something resembling black earth moistened with water, and death soon followed. That very night the Thunderers came, and the crashing sounds were so terrible that many people fainted. The next morning the shore was covered with the bodies of all kinds of fish, some of which were larger than men, and there were also some huge serpents. The water monster which the Thunderers fought resembled a rattle snake, but he had short legs and rusty-yellow fur.”
--J. Owen Dorsey, “Teton Folk-Lore Notes”, The Journal of American Folklore, Vol. 2 No. 5, 1889, pp. 133-139.