Exodus 7:15-18

15Go to Pharaoh in the morning. When you see him walking out to the water, stand ready to meet him by the bank of the Nile. Take in your hand the staff that turned into a snake.

16Tell him: The Lord, the God of the Hebrews, has sent me to tell you: Let my people go, so that they may worship me in the wilderness. But so far you have not listened.

17This is what the Lord says: Here is how you will know that I am the Lord. Watch. I am about to strike the water in the Nile with the staff in my hand, and it will turn to blood.

18The fish in the Nile will die, the river will stink, and the Egyptians will be unable to drink water from it.”