Sea between the straits

See Responsa Yechava Da’at, Part 1, Section 8:
Question: Is it permissible to swim in the sea or in the pool during the week of ​​ and ​ Tisha B’Av

Answer: In Tractate Ta’anit (page 30a), it is explained that there is no prohibition from the main halakhah to bathe even on the eve of Tisha B’Av, until the time of the meal that breaks the fast, however, the Jewish custom is to be strict in bathing even before Tisha B’Av, and as explained in the book Harokach (Siman 12b), our Rabbi Clonymus, a Roman, ruled that bathing is prohibited starting on the first day of the month of Av, and he also wrote in the book Pardes HaGadol (656) and in the book Shebuli HaLekt (657). And it is clear that the intention is not to prohibit bathing from the first day of the month of Av from the law, but from the custom, and as they said in the vows (15a), things that are permitted and others have practiced a prohibition in them, you are not permitted to permit them in their presence.

And regarding swimming in a pool or on the beach, when there is no fear of break-ins and no mixing of men and women at all, Medev ​​ According to the Maimonides and the Ramban, who did not prohibit during the week in which Tisha B’Av falls, only entering the bathhouse, that is, bathing in hot water, meaning that bathing in cold water is permitted, and there is no custom to be strict about this at all. And indeed, from the words of the Or Zura and Mordechai it seems that they believe in being strict even in the cold, but in the original of their words, in the Rabbis, it is explained that in the cold it is permissible in any case. And so the Gaon Rabbi Israel Israel testified in the Responsa Terumat Hadshan (6551), as he seems to have seen in his time of disgrace, that they were lenient in bathing in rivers from the beginning of the month of Av onwards, and the Sages did not wave their hand at them. And so the Gaon Rabbi Israel of Bruna wrote in the Teshuva (6512), that many are lenient in bathing in rivers on these days, and he was precise in this from the words of the Maimonides, who forbade only warm water, but in the cold it is permissible, and the reason is that due to the great heat found in the month of Av, people are filled with sweat, and it is obvious that if they do not bathe at least in the cold, they will be very sorry, and therefore they did not practice being strict in this. And so he testified in the Sefer Shulchan Gavo (6551, 48), that the custom in Salonika is to swim in the sea, even on the eve of Tisha B’Av, and there is no excuse. The Gaon Rabbi Chaim Pelaji also testified in the book Ruach Chaim (1751-177), about the custom of Izmir.

And indeed, there are some who have also become stricter about cold weather, and among them: in the book Mate Yehuda, and in the book Ben Ish Chai, in any case, since the entire basis of this harshness is not from the main halakhah but from the Torah of custom, and in the Land of Israel there is no clear custom in this regard among the Eastern communities, it seems that it is certainly necessary to instruct people to be lenient about swimming in the sea or in a pool or showering in cold weather, even in the week in which Tisha B’Av falls. And in any case, it seems that our Ashkenazi brothers who follow the example of the Rema should be even stricter about cold weather, and only for workers who return from their work drenched in sweat, and without a cold shower, they have great sorrow, they should be lenient about showering in cold weather.   It is true that there is reason to be cautious because of the words of the Shulchan Arba (O’ach 6′ Tikna 6′) that one must avoid things that are dangerous because of bitter Katab. I do not understand these matters, although I do not have much faith in these determinations.