Exodus 7:20

18The fish that are in the river will die and the river will become foul. The Egyptians will loathe to drink water from the river.”’”

19The LORD said to Moses, “Tell Aaron, ‘Take your rod, and stretch out your hand over the waters of Egypt, over their rivers, over their streams, and over their pools, and over all their ponds of water, that they may become blood. There will be blood throughout all the land of Egypt, both in vessels of wood and in vessels of stone.’”

20Moses and Aaron did so, as the LORD commanded; and he lifted up the rod, and struck 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.

21The fish that were in the river died. The river became foul. The Egyptians couldn’t drink water from the river. The blood was throughout all the land of Egypt.

22The magicians of Egypt did the same thing with their enchantments. So Pharaoh’s heart was hardened, and he didn’t listen to them, as the LORD had spoken.