Exodus 7:20-22

20And Moses and Aaron did so, as Jehovah commanded; and he lifted up the rod, and smote the waters that were in the river, in the sight of Pharaoh, and in the sight of his servants; and all the waters that were in the river were turned to blood. 21And the fish that were in the river died; and the river became foul, and the Egyptians could not drink water from the river; and the blood was throughout all the land of Egypt. 22And the magicians of Egypt did in like manner with their enchantments: and Pharaoh’s heart was hardened, and he hearkened not unto them; as Jehovah had spoken.