Rebbe Akiva used it to prove to an Apikores that shabbos has significance. There are wells that have predictable cycles. Perhaps there was such a well upstream that stayed high all week and created strong rapids.
Anyhow, this is what the Zemer, Yom Shabbos Kodesh Hu, refers to: Sambatyon Hanahar, Shebechol Yom Ratz Venimhar, Yochi’ach Bo Manoch, Tashiv Lemin Asher Sho’el.