The Lord told Moses he had made him like God to Pharaoh and that Aaron his brother would be his prophet. Moses was to say all that God commanded, and Aaron would say it to Pharaoh. God would harden Pharaoh's heart and multiply his signs and wonders in Egypt, but Pharaoh would not listen to them. Then God would lay his hand on Egypt and bring out his people by great acts of judgment, and the Egyptians would know that he is the Lord. Moses was eighty and Aaron eighty-three when they spoke to Pharaoh.
When Pharaoh asked for a sign, Aaron threw down his staff before him and his servants, and it became a serpent. Pharaoh called his wise men and sorcerers, and the magicians of Egypt did the same with their secret arts, but Aaron's staff swallowed theirs. Still, Pharaoh's heart was hardened and he would not listen, as the Lord had said.
The Lord then told Moses to go to Pharaoh in the morning as he went out to the river, to stand on the bank with the staff that had turned into a serpent and tell him that the God of the Hebrews had sent him to say let my people go; since Pharaoh had not obeyed, by this he would know that the Lord is God: Moses would strike the water of the river and it would turn to blood. The fish would die, the river would stink and the Egyptians could not drink from it.
Aaron stretched out his staff over the waters of Egypt, the rivers, canals, ponds and all the reservoirs, and all the water turned to blood, even in wooden and stone vessels. The fish died and the river stank. The magicians of Egypt did the same with their secret arts, and Pharaoh's heart stayed hard. He turned and went into his house, giving no thought to this, and the Egyptians dug along the river for water to drink. Seven days passed after the Lord struck the river.