Exodus 7:19-22

19And the LORD said to Moses, “Tell Aaron, ‘Take your staff and stretch out your hand over the waters of Egypt—over their rivers and canals and ponds and all the reservoirs—that they may become blood.’ There will be blood throughout the land of Egypt, even in the vessels of wood and stone.”

20Moses and Aaron did just as the LORD had commanded; in the presence of Pharaoh and his officials, Aaron raised the staff1 and struck the water of the Nile, and all the water was turned to blood. 21The fish in the Nile died, and the river smelled so bad that the Egyptians could not drink its water. And there was blood throughout the land of Egypt.

22But the magicians of Egypt did the same things by their magic arts. So Pharaoh’s heart was hardened, and he would not listen to Moses and Aaron, just as the LORD had said.