The first mighty act of God serves in the narrative as a paradigm of the nine plagues that follow. Striking the Nile with the rod suggested dominion over creation and all the gods of Egyptian mythology. The Egyptians linked many of their gods with the life-giving force of the Nile. The tenth plague is unique in that it is both a part of the narrative of Exodus as a whole and is a mighty act of God in itself. [1][source]
Evidently Pharaoh had his morning devotions on the banks of the sacred Nile River. Moses and Aaron met him there as he prepared to honor the gods of the river ( Exodus 7:15). [source][source][source]
We could perhaps interpret the statement that the water turned into blood ( Exodus 7:20) in the same way we interpret Joel"s prophecy that the moon will turn into blood ( Joel 2:31 cf. Revelation 6:12). Moses may have meant that the water appeared to be blood. [2] Nevertheless something happened to the water to make the fish die. The Hebrew word translated "blood" means blood, so a literal meaning is possible. [3] Furthermore the passage in Joel is poetry and therefore figurative, whereas the passage here in Exodus is narrative and may be understood literally. [4] Note too that this plague affected all the water in pools and reservoirs formed by the overflowing Nile as well as the water of the Nile and its estuaries ( Exodus 7:19). Understood figuratively or literally a real miracle took place, as is clear from the description of the effects this plague had on the Egyptians and the fish in the Nile. The Egyptian wizards were able to duplicate this wonder, but they could not undo its effects. [source][source][source]
"The most that can be said for their miracle-working is that it is a copy of what Moses and Aaron have accomplished and that it actually makes matters worse for their master and their people." [5][source]
"It was appropriate that the first of the plagues should be directed against the Nile River itself, the very lifeline of Egypt and the center of many of its religious ideas. The Nile was considered sacred by the Egyptians. Many of their gods were associated either directly or indirectly with this river and its productivity. For example, the great Khnum was considered the guardian of the Nile sources. Hapi was believed to be the "spirit of the Nile" and its "dynamic essence." One of the greatest gods revered in Egypt was the god Osiris who was the god of the underworld. The Egyptians believed that the river Nile was his bloodstream. In the light of this latter expression, it is appropriate indeed that the Lord should turn the Nile to blood! It is not only said that the fish in the river died but that the "river stank," and the Egyptians were not able to use the water of that river. That statement is especially significant in the light of the expressions which occur in the "Hymn to the Nile": "The bringer of food, rich in provisions, creator of all good, lord of majesty, sweet of fragrance". [6] With this Egyptian literature in mind, one can well imagine the horror and frustration of the people of Egypt as they looked upon that which was formerly beautiful only to find dead fish lining the shores and an ugly red characterizing what had before provided life and attraction. Crocodiles were forced to leave the Nile. One wonders what worshipers would have thought of Hapi the god of the Nile who was sometimes manifest in the crocodile. Pierre Montet relates the following significant observation:[source]
""At Sumenu (the modern Rizzeigat) in the Thebes area, and in the central district of the Fayum, the god Sepek took the form of a crocodile. He was worshipped in his temple where his statue was erected, and venerated as a sacred animal as he splashed about in his pool. A lady of high rank would kneel down and, without the slightest trace of disgust, would drink from the pool in which the crocodile wallowed. Ordinary crocodiles were mummified throughout the whole of Egypt and placed in underground caverns, like the one called the Cavern of the Crocodiles in middle Egypt." [2][source]
"Surely the pollution of the Nile would have taken on religious implications for the average Egyptian. Those who venerated Neith, the eloquent warlike goddess who took a special interest in the lates, the largest fish to be found in the Nile, would have had second thoughts about the power of that goddess. Nathor was supposed to have protected the chromis, a slightly smaller fish. Those Egyptians who depended heavily on fish and on the Nile would indeed have found great frustration in a plague of this nature." [8][source]
"Each year, toward the end of June, when the waters of the Nile begin to rise, they are colored a dark red by the silt carried down from the headwaters. This continues for three months, until the waters begin to abate, but the water, meanwhile, is wholesome and drinkable. The miracle of Exodus 7:17-21 involved three elements by which it differed from the accustomed phenomenon: the water was changed by the smiting of Moses" rod; the water became undrinkable; and the condition lasted just seven days ( Exodus 7:25)." [9][source]
The commentators have interpreted the reference to blood being throughout all Egypt "in (vessels of) wood and in (vessels of) stone" ( Exodus 7:19) in various ways. Some believe this refers to water in exterior wooden and stone water containers. Others think it refers to water in all kinds of vessels used for holding water. Still others believe Moses described the water in trees and in wells. However this expression may refer to the water kept in buildings that the Egyptians normally constructed out of wood and stone. [source][source][source]
"In the Bible a totality is more often indicated by mentioning two fundamental elements; see e.g, "milk and honey" (Ex. iii8 , etc.) and "flesh and blood" (Matt. xvi17)." [10][source]
This is a synecdoche, a figure of speech in which a part stands for the whole or the whole represents a part. The quotation above supports the idea that God changed even the water stored in buildings to blood. [source][source][source]
"Each of the first nine of the mighty-act accounts may be said to have the same fundamental point, expressed in much the same way. That point, concisely summarized, is that Yahweh powerfully demonstrates his Presence to a Pharaoh prevented from believing so that Israel may come to full belief." [11][source]