Exodus 7:20 – 22
New International Version (NIV)
20 Moses and Aaron did just as the LORD had commanded. He raised his staff in the presence of Pharaoh and his officials and struck the water of the Nile, and all the water was changed into blood. 21 The fish in the Nile died, and the river smelled so bad that the Egyptians could not drink its water. Blood was everywhere in Egypt.
22 But the Egyptian magicians did the same things by their secret arts, and Pharaoh's heart became hard; he would not listen to Moses and Aaron, just as the LORD had said.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=Exodus+7.20-22&version=NIV