Adam Clarke on Exodus 7:15

Lo, he goeth out unto the water - Probably for the purpose of bathing, or of performing some religious ablution. Some suppose he went out to pay adoration to the river Nile, which was an object of religious worship among the ancient Egyptians. "For," says Plutarch, De Iside., ουδεν οὑτω τιμη Αιγυπτιοις ὡς ὁ Νειλος "nothing is in greater honor among the Egyptians than the river Nile." Some of the ancient Jews supposed that Pharaoh himself was a magician, and that he walked by the river early each morning for the purpose of preparing magical rites, etc.