Exodus 7:15-18

15Go unto Pharaoh in the morning — behold, he will go out unto the water — and take thy stand by the bank of the river in front of him; and take in thy hand the staff that was turned into a serpent.

16And say unto him, Jehovah the 1God of the Hebrews has sent me to thee, saying, Let my people go, that they may serve me in the wilderness; but behold, hitherto thou hast not hearkened.

17Thus saith Jehovah: In this shalt thou know that I am Jehovah — behold, I will smite with the staff that is in my hand upon the water which is in the river, and it shall be turned into blood.

18And the fish that is in the river shall die; and the river shall stink; and the Egyptians shall loathe to drink the water out of the river.