אָ֚ז אַשְׁקִ֣יעַ מֵֽימֵיהֶ֔ם וְנַהֲרוֹתָ֖ם כַּשֶּׁ֣מֶן אוֹלִ֑יךְ נְאֻ֖ם אֲדֹנָ֥י יְהוִֽה׃
Then will I make their waters to settle, And cause their rivers to run like oil, Saith the Lord GOD.
Rashi on Ezekiel
I shall sink their waters The foot of cattle will not make it murky, and the mud will sink, so that the water will be clear and clean like refined oil.