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, over their pools, and over all their reservoirs of water, so that they may become blood; and there shall be blood throughout all the land of Egypt, in containers both of wood and of stone.’ ” So Moses and Aaron did as the LORD commanded; Aaron lifted up the staff and struck the waters 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 into blood.