Exodus 7:16-18

Young's Literal Translation

¹⁶ and thou hast said unto him: Jehovah, God of the Hebrews, hath sent me unto thee, saying, Send My people away, and they serve Me in the wilderness; and lo, thou hast not hearkened hitherto.

¹⁷ `Thus said Jehovah: By this thou knowest that I [am] Jehovah; lo, I am smiting with the rod which [is] in my hand, on the waters which [are] in the River, and they have been turned to blood,

¹⁸ and the fish that [are] in the River die, and the River hath stank, and the Egyptians have been wearied of drinking waters from the River.'