Exodus 7:14-25

Then the Lord said to Moses, Pharaoh's heart is hard and stubborn; he refuses to let the people go. Go to Pharaoh in the morning; he will be going out to the water; wait for him by the river's brink; and the rod which was turned to a serpent you shall take in your hand. And say to him, The Lord, the God of the Hebrews has sent me to you, saying, Let My people go, that they may serve Me in the wilderness; and behold, heretofore you have not listened. Thus says the Lord, In this you shall know, recognize, and understand that I am the Lord: behold, I will smite with the rod in my hand the waters in the [Nile] River, and they shall be turned to blood. The fish in the river shall die, the river shall become foul smelling, and the Egyptians shall loathe to drink from it. And the Lord said to Moses, Say to Aaron, Take your rod and stretch out your hand over the waters of Egypt, over their streams, rivers, pools, and ponds of water, that they may become blood; and there shall be blood throughout all the land of Egypt, in containers both of wood and of stone. Moses and Aaron did as the Lord commanded; [Aaron] lifted up the rod and smote the waters in the river in the sight of Pharaoh and his servants, and all the waters in the river were turned to blood. And the fish in the river 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. But the magicians of Egypt did the same by their enchantments and secret arts; and Pharaoh's heart was made hard and obstinate, and he did not listen to Moses and Aaron, just as the Lord had said. And Pharaoh turned and went into his house; neither did he take even this to heart. And all the Egyptians dug round about the river for water to drink, for they could not drink the water of the [Nile]. Seven days passed after the Lord had smitten the river.