Siman 200

Every woman is obligated to bless at the time of her tevilah, and even one who sits due to a ketem, which is rabbinic, blesses "Who has sanctified us with His mitzvot and commanded us regarding the tevilah," for even regarding rabbinic matters "and commanded us" is applicable, from that which is written: "You shall not deviate from the matter that they tell you," etc. [Shabbat 23a]. And even one who sits due to blood of purity, which is merely a general custom, blesses, since all of Israel have accepted this stringency upon themselves, and it is no less than Hallel on Rosh Chodesh, upon which we bless [see Tosafot [Berakhot 14a]]. And even for a doubtful ketem she blesses, and there is no tevilah without a blessing, except when she immersed and afterward returns and immerses due to some stringency, such as if she forgot to trim a nail or the like, she immerses without a blessing.

And she recites the blessing "...Who has sanctified us with His commandments and commanded us concerning the immersion." And it is not only necessary according to those who hold that she recites the blessing after she has immersed, but even according to those who hold that she recites the blessing prior to the immersion, as will be explained. And according to this, following the sugya of the Shas in Pesachim [7b] and the Rambam in the eleventh chapter of Hilkhot Berakhot, she should have recited the blessing "to immerse" with the letter Lamed and not "concerning the immersion." Nevertheless, since there is the immersion of a convert [in ancient times] who recites the blessing after the immersion—as beforehand he cannot say "and commanded us," as is understood—and he is perforce required to recite the blessing "concerning the immersion" since it is after the act, therefore the sages did not differentiate among all immersions, and they recite the blessing "concerning the immersion" [meaning there; and even though from the Rambam there it appears to me that she should recite the blessing "to immerse," see there as he did not mention this, yet from all the poskim it is explained like the Ran; and examine this closely].

It was taught in Pesachim ibid.: If one immersed and ascended, upon his ascension he says "Blessed etc." And it is also stated there previously: For all mitzvot, one recites the blessing over them prior to their performance, except for immersion. According to the explanation of Rashi, this refers to all immersions, see there. However, the Rif wrote there that it refers only to the immersion of a convert for the reason that has been explained, but all those obligated in immersion recite the blessing prior to the immersion. The Rambam also wrote so there. This is the wording of our teacher, the Beit Yosef: When she removes her garments, while she is standing in her shift, she should recite the blessing "...Who has sanctified us with His mitzvot and commanded us concerning the immersion," and then remove her shift and immerse. If she did not recite the blessing then, she should recite the blessing after she enters the water up to her neck; and if the waters are clear, she should stir them with her feet and recite the blessing. Thus far his words. The reason is so that her heart does not see the nakedness [Levush]. However, in Orach Chaim siman 74 it is explained that for a woman this prohibition does not exist because her nakedness is below, see there. Rather, it appears the reason is that even though it is not a requirement that invalidates, nevertheless it is not the way of honor for Heaven to mention the Name while her entire body appears naked [see Taz subsection 1, and according to what I wrote it is well understood, and examine it closely].

But our teacher, the Rema, wrote: And there are those who say that she should not bless until after the immersion, and such is the custom, that after the immersion, while she is still standing within the water, she covers herself with her garment or her robe and blesses. Thus far his words. And there are those who wrote that she should cross her arms to create a separation between her heart and her nakedness while she is within the water and blesses. But our women do not do so, and they bless even in clear water with their eyes outside the water, and they do not cover themselves and do not cross their arms. And there is one who complained about this, saying that even though there is no concern of the heart seeing the nakedness, as has been written, nevertheless, since the water is clear, it is as if she is standing naked, and it is forbidden to mention the Name. And they rejected his words, for a person standing in water, even clear water, is not like one standing naked, for the water acts as a covering even when it is clear, and there is no concern here of "and He shall not see among you an unseemly thing," for it is for this reason that it is forbidden to mention the Name when one is naked, as was written in Orach Chaim there. And so wrote our teacher, the Beit Yosef, in his great book in Orach Chaim siman 206 in the name of the Rashba, that when one's eyes are outside the water, there is no concern of nakedness; see there. And know that the custom of our women is that they immerse once and bless, and afterward they immerse a second time, and with this they fulfill all opinions, so that the blessing is before the immersion and after the immersion, and it is a beautiful custom.