Mikvaot, Chapter Five, Mishnah Four
Our mishnah deals with the status of the seasdo they count as a mikveh or as living waters?
The exact same mishnah is found in Parah 8:8. Most of my commentary is the same as it was there.
1) All seas are equivalent to a mikveh, for it is said, “And the gathering (ulemikveh) of the waters He called the seas” (Genesis 1:10), the words of Rabbi Meir.
2) Rabbi Judah says: only the Great Sea is equivalent to a mikveh, for it says “seas” only because there are in it many kinds of seas.
3) Rabbi Yose says: all seas afford cleanness when running, and yet they are unfit for zavim and metzoraim and for the preparation of the hatat waters.
Section one: According to Rabbi Meir the seas are considered to be like a mikveh and not like a flowing spring, which can be used for the red cow, for zavim (those with unusual genital discharge) and for metzoraim (those with scale disease), all of whom require “living waters.” In contrast to the rules governing a spring, for a mikveh to purify the water must be gathered into one place and it cannot be running. The seas are treated like a mikveh and therefore its waters purify only when they are gathered in one place. Rabbi Meir learns this from a midrash on the word “gathering” which is in Hebrew, mikveh. Genesis calls the seas a mikveh and therefore they are subject to the same rules as a mikveh and not to the rules of a live spring.
Section two: In contrast, Rabbi Judah limits this to the ocean, which in his case is the Mediterranean. Other seas are treated like springs and purify even when they are running. He explains that Genesis states “seas” not because it refers to all seas as a mikveh. Rather the Mediterranean is “seas” because it contains many different seas. One interpretation of this is that a fish that is caught in Akko does not have the same taste as a fish that is caught in Sidon!
Section three: Rabbi Yose says that all seas can purify when they are runningnone have the same restrictions as do a mikveh. However, the seas are not considered to be “living waters” as would be a spring. Therefore, none of the seas can be used for any of the rituals that requires “living waters”the red cow, zavim and metzoraim.