Exodus 7:17-18

So the Lord says, By this you may be certain that I am the Lord; see, by the touch of this rod in my hand the waters of the Nile will be turned to blood; And the fish in the Nile will come to destruction, and the river will send up a bad smell, and the Egyptians will not be able, for disgust, to make use of the water of the Nile for drinking.