לֵךְ אֶל פַּרְעֹה בַּבֹּקֶר הִנֵּה יוֹצֵא הַמַּיְמָה, לֹא הָיָה יוֹצֵא אֶלָּא הַמַּיְמָה בַּבֹּקֶר, לְפִי שֶׁאוֹתוֹ רָשָׁע הָיָה מִשְׁתַּבֵּחַ וְאוֹמֵר שֶׁהוּא אֱלוֹהַּ וְאֵינוֹ יוֹצֵא לִנְקָבָיו, לְפִיכָךְ הָיָה יוֹצֵא בַּבֹּקֶר, בְּשָׁעָה שֶׁהוּא נִצְרַךְ תְּפֹשׂ אוֹתוֹ. וְהַמַּטֶּה אֲשֶׁר נֶהְפַּךְ לְנָחָשׁ תִּקַּח בְּיָדֶךָ, כְּדֵי שֶׁיִּתְיָרֵא מִמֶּנּוּ.
.... לָמָּה לָקוּ הַמַּיִם תְּחִלָּה בְּדָם, מִפְּנֵי שֶׁפַּרְעֹה וְהַמִּצְרִיִּים עוֹבְדִים לַיְאוֹר, אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא אַכֶּה אֱלוֹהַּ תְּחִלָּה וְאַחַר כָּךְ עַמּוֹ, מָשָׁל הֶדְיוֹט אוֹמֵר מְחֵי אֱלָהַיָא וְיִבָּעֲתוּן כֻּמְרַיָא....
(טו) הנה יוצא המימה - כדרך השרים לטייל בבקר ולרכוב אנה ואנה.
(15) הנה יוצא המימה, as do most ministers, in order to take their morning stroll. Sometimes they go for a short gallop on their horse.
(א) לך אל פרעה בבקר. מנהג מלך מצרים עד היום לצאת בתמוז ואב כי אז יגדל היאור לראות כמה מעלות עלה.
(1) GET THEE UNTO PHARAOH IN THE MORNING. It is the custom of the king of Egypt until this very day to go out in the months of Tamuz and Ab to see how high the water has risen.
וַאֲמַר אֲבִיטוּל סָפְרָא מִשְּׁמֵיהּ דְּרַב פָּפָּא פַּרְעֹה שֶׁהָיָה בִּימֵי מֹשֶׁה אַמְגּוּשִׁי הָיָה שֶׁנֶּאֱמַר הִנֵּה יוֹצֵא הַמָּיְמָה וְגוֹ׳:
Avitul the scribe also said in the name of Rav Pappa: The Pharaoh who lived in the days of Moses was a sorcerer [amgushi], as it is stated: “Behold, he goes out to the water” (Exodus 7:15). Pharaoh would regularly go out to the water in order to engage in witchcraft.
See Wilkinson's "Complete Gods...of Ancient Egypt"
re Hapy - pp. 106- 109; re Maat - pp. 150-152
LITERARY AND STYLISTIC ELEMENTS OF THE TEN PLAGUES
Couplet interpretation of the ten:
1-2: involved the Nile waters (blood, frogs)
3-4: involved insects (lice, swarms)
5-6: involved illness: ("dever" (disease), boils)
7-8: ruined crops (hail, locusts)
9-10: darkness: (darkness; death of firstborn at midnight)
Tripartite interpretation of the ten (three sets of three plus #10):
1,4,7: G charged Moshe to "station self" before Pharoah (Hebrew root "N-Tz-V") during morning time;
2,5,8: Moshe told to come/go ("bo") to Pharoah;
In each set, the 1st and 2nd plague of set is forewarned; 3rd is not.
Aharon is the agent in the first set; Moshe performs the final three.
Robert Alter: "This narrative presupposes...that Egyptian royalty regularly went down to the Nile to bathe, unless the purposes was, as ibn Ezra proposes, to check the level of the Nile.
Pharoah's encounter with Moses by the riverside looks back to the discovery of Moses by Pharoah's daughter when she went down to the Nile."
MOSHE'S ASSOCIATION WITH THE NILE
Moshe's initial connection: it was to be the context for his (possible) demise (in the basket).
At the bank of the Nile he encountered a member of the ethnic group committed to the decimation of the Israelites.
Yet, Pharoah's daughter rescued him from the Nile.
NILE = MOTIVE IN THE EGYPTIAN SAGA: REVERSAL OF FATE.
As with Moshe, so too the nation of Israel. The Reed Sea which should destroy the people Israel become their passageway, and the Egyptians drown in the waters.
Nahum Sarna (JPS Exodus):
The controlling purpose behind this literary architecture is to emphasize the idea that the nine plagues are not random vicissitudes of nature; although they are are natural disasters, they are the deliberate and purposeful acts of divine will - their intent being retributive, coercive, and educative. As God's judgments on Egypt for the enslavement of the Israelites, they are meant to crush Pharoah's resistance to their liberation. They are to demonstrate to Egypt the impotence of its gods and, by contrast, the incomparability of YHVH, God of Israel, as the one supreme sovereign God of Creation, who uses the phenomena of the natural order for His own purposes.
Also see Scott Noegel, "Why Pharoah Went to the Nile," in Torah.com.