Moses and Aaron were directed to visit the riverside next morning, where the king was accustomed to repair. The overflowing of the Nile being the source of food and wealth for all Egypt, the river was worshiped as a god, and the monarch came thither daily to pay his devotions. Here the two brothers again repeated the message to him, and then they stretched out the rod and smote upon the water. The sacred stream ran blood, the fish died, and the river became offensive to the smell. The water in the houses, the supply preserved in cisterns, was likewise changed to blood. But "the magicians of Egypt did so with their enchantments," and "Pharaoh turned and went into his house, neither did he set his heart to this also." For seven days the plague continued, but without effect.

Moses og Aron fik befaling om at gå ned til flodbredden næste morgen. Her plejede kongen at komme. Da Nilen ved sine oversvømmelser skaffede hele Ægypten føde og rigdom, blev den tilbedt som en gud, og kongen gik daglig ned til floden for at tilbede. Her gentog de to brødre deres budskab til ham, hvorpå de rakte staven ud og slog på vandet. Flodens hellige vand blev til blod, fiskene døde, og floden begyndte at stinke. Vandet i husene og cisternerne blev også forvandlet til blod. Men de ægyptiske koglere gjorde det samme ved hjælp af deres hemmelige kunster og Farao vendte sig bort og gik hjem, og heller ikke dette lagde han sig på sinde. Plagen varede i syv dage, men var uden virkning.