וְהַדָּגָ֧ה אֲשֶׁר־בַּיְאֹ֛ר תָּמ֖וּת וּבָאַ֣שׁ הַיְאֹ֑ר וְנִלְא֣וּ מִצְרַ֔יִם לִשְׁתּ֥וֹת מַ֖יִם מִן־הַיְאֹֽר׃ (ס)
And the fish that are in the river shall die, and the river shall become foul; and the Egyptians shall loathe to drink water from the river.’
Read halakhic rulings (Jewish law) on Exodus 7:18 from the Mishneh Torah and classical halakhic sources, free online.