Exodus 7:14-18

Then the Lord said to Moses, “Pharaoh’s heart is stubborn; he refuses to let the people go.

Go to Pharaoh in the morning just as he is going out to the water, and position yourself to meet him on the bank of the Nile; and you shall take in your hand the staff that was turned into a serpent.

And you shall say to him, ‘The Lord, the God of the Hebrews, sent me to you, saying, “Let My people go, so that they may serve Me in the wilderness. But behold, you have not listened up to now.”

This is what the Lord says: “By this you shall know that I am the Lord: behold, I am going to strike the water that is in the Nile with the staff that is in my hand, and it will be turned into blood.

Then the fish that are in the Nile will die, the Nile will stink, and the Egyptians will no longer be able to drink water from the Nile.” ’ ”