Exodus 7:17

14 And the Lord said to Moses and Aaron, Pharaoh's heart is unchanged; he will not let the people go.

15 Go to Pharaoh in the morning; when he goes out to the water, you will be waiting for him by the edge of the Nile, with the rod which was turned into a snake in your hand;

16 And say to him, The Lord, the God of the Hebrews, has sent me to you, saying, Let my people go so that they may give me worship in the waste land; but up to now you have not given ear to his words.

17 So the Lord says, By this you may be certain that I am the Lord; see, by the touch of this rod in my hand the waters of the Nile will be turned to blood;

18 And the fish in the Nile will come to destruction, and the river will send up a bad smell, and the Egyptians will not be able, for disgust, to make use of the water of the Nile for drinking.

19 And the Lord said, Say to Aaron, Let the rod in your hand be stretched out over the waters of Egypt, and over the rivers and the streams and the pools, and over every stretch of water, so that they may be turned to blood; and there will be blood through all the land of Egypt, in vessels of wood and in vessels of stone.

20 And Moses and Aaron did as the Lord had said; and when his rod had been lifted up and stretched out over the waters of the Nile before the eyes of Pharaoh and his servants, all the water in the Nile was turned to blood;