Exodus 7:17

14 And the Lord said to Moses: Pharao's heart is hardened, he will not let the people go.

15 Go to him in the morning, behold he will go out to the waters: and thou shalt stand to meet him on the ' bank of the river: and thou shalt take in thy hand the rod that was turned into a serpent.

16 And thou shalt say to him: The Lord God of the Hebrews sent me to thee, saying: Let my people go to sacrifice to me in the desert: and hitherto thou wouldst not hear.

17 Thus therefore saith the Lord: In this thou shalt know that I am the Lord: behold I will strike with the rod, that is in my hand, the water of the river, and it shall be turned into blood.

18 And the fishes that are in the river, shall die, and the waters shall be corrupted, and the Egyptians shall be afflicted when they drink the water of the river.

19 The Lord also said to Moses: Say to Aaron, Take thy rod; and stretch forth thy hand upon the waters of Egypt, and upon their rivers, and streams and pools, and all the ponds of waters, that they may be turned into blood: and let blood be in all the land of Egypt, both in vessels of wood and of stone.

20 And Moses and Aaron did as the Lord had commanded: and lifting up the rod, he struck the water of the river before Pharao and his servants: and it was turned into blood.