Genesis 2:14

חדקל TIGRIS — It is called חדקל because its waters are pungent in taste (חד) and light in weight (קל) (Berakhot 59b). פרת EUPHRATES — It is called פרת because its waters grow (פרה) and increase and make men healthy (Berakhot 59b). כוש ואשור CUSH AND ASHUR did not then exist as countries, but Scripture writes with reference to the names which those districts would bear in the future (Ketubot 10b; Genesis Rabbah 16). קדמת אשור means AT THE EAST OF ASHUR. הוא פרת IS THE EUPHRATES — the most important of all, being mentioned in connection with the Land of Israel (Genesis Rabbah 16:3).

וְשֵׁ֨ם הַנָּהָ֤ר הַשְּׁלִישִׁי֙ חִדֶּ֔קֶל ה֥וּא הַֽהֹלֵ֖ךְ קִדְמַ֣ת אַשּׁ֑וּר וְהַנָּהָ֥ר הָֽרְבִיעִ֖י ה֥וּא פְרָֽת׃

And the name of the third river is Ḥiddeqel: that is it which goes toward the east of Ashshur. And the fourth river is Perat.