Exodus 7:20-22

20Moses and Aaron did as the Lord had commanded. In front of Pharaoh and his officials, Aaron raised his staff and struck the Nile. All the water in the river turned into blood.

21The fish in the Nile died, and it smelled so bad that the Egyptians couldn’t drink any water from the river. There was blood everywhere in Egypt.

22But the Egyptian magicians did the same thing using their magic spells. So Pharaoh continued to be stubborn and would not listen to Moses and Aaron, as the Lord had predicted.