Exodus 7:19-20

Then the LORD said to Moses, “Say to Aaron, ‘Take your staff and stretch out your hand over the waters of Egypt, over their rivers, over their streams, and over their pools, and over all their reservoirs of water, that they may become blood; and there will be blood throughout all the land of Egypt, both in vessels of wood and in vessels of stone.’ ” So Moses and Aaron did even as the LORD had commanded. And he lifted up the staff and struck the water that was in the Nile, in the sight of Pharaoh and in the sight of his servants, and all the water that was in the Nile was turned to blood.