Exodus 7:17-21

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.”

19So the Lord said to Moses, “Tell Aaron: Take your staff and stretch out your hand over the waters of Egypt — over their rivers, canals, ponds, and all their water reservoirs — and they will become blood. There will be blood throughout the land of Egypt, even in wooden and stone containers.”

20Moses and Aaron did just as the Lord had commanded; in the sight of Pharaoh and his officials, he raised the staff and struck the water in the Nile, and all the water in the Nile was turned to blood.

21The fish in the Nile died, and the river smelled so bad the Egyptians could not drink water from it. There was blood throughout the land of Egypt.