Exodus 7:20-25

20And Moses and Aaron did so, as the LORD commanded; and he lifted up the rod, and smote the waters that were in the river, in the sight of Pharaoh, and in the sight of his servants; and all the waters that were in the river were turned to blood. 21And the fish that was in the river died; and the river stank, and the Egyptians could not drink water from the river; and the blood was throughout all the land of Egypt. 22And the magicians of Egypt did in like manner with their enchantments: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the LORD had spoken. 23And Pharaoh turned and went into his house, neither did he lay even this to heart. 24And all the Egyptians digged round about the river for water to drink; for they could not drink of the water of the river. 25And seven days were fulfilled, after that the LORD had smitten the river.