Exodus 7:20-22

20So Moses and Aaron did as the Lord commanded; Aaron lifted up the staff and struck the waters in the Nile, in the sight of Pharaoh and in the sight of his servants, and all the water that was in the Nile was turned into blood.

21The fish in the Nile died, and the river became foul smelling, and the Egyptians could not drink its water, and there was blood throughout all the land of Egypt.

22But the magicians of Egypt did the same by their secret arts and enchantments; so Pharaoh’s heart was hardened, and he did not listen to Moses and Aaron, just as the Lord had said.