1)
What is "Meichal ha'Mayim"?
1.
Rashi: I do not know a root 'Kol' (the letters Chaf Lamed, for the word Meichal); from context, it is like Shiboles ha'Nahar (where the river flows rapidly).
2.
Radak: It is where the water separates (branches into two tributaries).
3.
Radak citing Targum Yonasan: It is the Yarden.
