Exodus 7:20-22

20So Moses and Aaron did just as the Lord commanded them. As Pharaoh and all of his officials watched, Aaron raised his staff and struck the water of the Nile. Suddenly, the whole river turned to blood!

21The fish in the river died, and the water became so foul that the Egyptians couldn’t drink it. There was blood everywhere throughout the land of Egypt.

22But again the magicians of Egypt used their magic, and they, too, turned water into blood. So Pharaoh’s heart remained hard. He refused to listen to Moses and Aaron, just as the Lord had predicted.