Mishnà su Genesi 1:10

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. 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. 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.

All seas are equivalent to a ritual bath (mikveh), for it is said, "And the gathering (ulemikveh) of the waters He called the seas" (Genesis 1:10), the words of Rabbi Meir. Rabbi Judah says: only the Great Sea is equivalent to a ritual bath, for it says "seas" only because there are in it many kinds of seas. 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.

All garments can contract the uncleanness of negaim except those of non-Jews. One who buys garments [with signs of negaim] from non-Jews they must be inspected as if the signs had then first appeared. The hides [of animals] of the sea do not contract the uncleanness of negaim. If one joined to them anything which grows on land, even if it is only a thread or a cord, as long as it is something that is susceptible to uncleanness, they also become susceptible to uncleanness.