Exodus 7:20-21

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. The fish in the Nile died, and the river became foul smelling, and the Egyptians could not drink its water, and there was blood throughout all the land of Egypt.