דַּבֵּר וְאָמַרְתָּ כֹּה אָמַר אֲדֹ-נָי ה' הִנְנִי עָלֶיךָ פַּרְעֹה מֶלֶךְ-מִצְרַיִם הַתַּנִּים הַגָּדוֹל הָרֹבֵץ בְּתוֹךְ יְאֹרָיו אֲשֶׁר אָמַר לִי יְאֹרִי וַאֲנִי עֲשִׂיתִנִי
Speak, saying, “Thus says the L-rd Hashem: behold, I am against you, Pharaoh, King of Egypt, the great crocodile that lies in the midst of his rivers, who has said, ‘My river is my own and I made it for myself.’ ”
Why is Pharoah compared to a crocodile of all things? Rashi explains that it is because of Egypt’s dependence on the Nile. Since all of Egypt’s success and prosperity comes from the river, the prophet uses the crocodile as a metaphor for Pharaoh and, in verse 4, fish as a metaphor for the Egyptian people.