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10. Swimming on Shabbos:
Introduction: Although bathing in cold water is customarily forbidden on Shabbos, as explained in the previous Halachos, nevertheless it may be done in certain scenarios, such as for the sake of Mikveh, or to relieve pain and the like. [See Halacha 4] Although it is permitted to enter the body of water in these cases, it is nevertheless forbidden from the letter of the law to swim in certain areas. Thus, in all cases mentioned that bathing in cold water is allowed one may not swim in those waters in the cases mentioned here to which the swimming prohibition applies. Furthermore, as will be explained in the Q&A, even in those areas where swimming is allowed from the letter of the law, it is forbidden to swim today due to the custom against bathing even in cold water. This applies even if one entered the water to use as a Mikveh.
The law: One may not swim [See Q&A on the definition of swimming] on the surface of water [that is in a river or certain pools as will be explained].
The reason for this is: due to a decree that one may come to make a barrel [that is normally used by] swimmers. This [instrument] refers to a vessel made from reeds which are woven and are made like an elongated barrel of which one learns to swim with.
A river: However, when does the above [suspicion and stringency] apply? [when swimming] in a river.
Swimming in a vessel: However when [swimming] in a vessel [this suspicion does not apply and] it is [thus] allowed [to swim in it] being that it is not common to make a barrel to swim with inside of a vessel.
A Pool without an external rim: However [to swim] in a pool in one’s courtyard is forbidden. [See Q&A if one may enter the pool if he will not swim in it]
The reason for this is: because when the water overflows upon one swimming, [the waters] leave the pool and this is similar to a river.
A pool with an external rim: [However] if the pool has an [external] rim around it [See Q&A regarding the definition], it is permitted to swim in it as even if the water overflows the rim returns the water to its place [in the pool] and it is thus similar to [swimming in] a vessel [as opposed to a river]. [See Q&A regarding of this ruling applies even if the pool is in a public area, and regarding if this leniency at all applies today when the custom is to never bathe in cold water!]
It is forbidden from the letter of the law to swim in a river or a pool which does not contain a slanted rim. A pool with a slanted rim, or a vessel which contains water, does not contain a swimming prohibition, [although based on the custom today not to bathe in cold water, it remains forbidden to swim in it due to this custom. This includes even a case that one was allowed to enter the pool even based on the custom, such as he entered to use it as a Mikveh or due to it being very hot, even so one is not to swim in it. However, in all cases where bathing in cold water is allowed even according to the custom, it is allowed to enter into any swimming pool, even without a rim, or even into a river, so long as one does not swim in it or tread water.]
What is the definition of swimming?
The lifting of both of one’s feet off the floor of the pool/river and to thus tread the water or swim it with ones hands is defined as swimming.
May one enter into a non–rimmed pool if he will not swim in it?
So long as one is allowed to do so even according to the custom to avoid bathing in cold water, [such as for Mikveh or on hot day] it is permitted to enter into a pool even if it is not rimmed, so long as one does not swim in it or tread water.
Q&A on rimmed pool
What is defined as a rim for the pool/What is the law if a pool is not filled to the top?
A rim refers to a walled area which surrounds the pool and prevents any water from leaving the pool, as even if it leaves, the rimmed area will cause the water to come back in. However, those pools which do not have this rimmed area surrounding the pool, are considered to be “rimless” in this regard, even if they are not filled to their top and thus no water will splash out. Thus most pools today do not carry the allowance to swim in them being that they do not contain an external rim.
If a rimmed pool is in a public area may one swim in it in cases that one is allowed to bathe in cold water?
Some Poskim rule that doing so is forbidden due to a suspicion that perhaps some of the water will splash outside of the 4 cubit radius of the pool and he will thus transgress the carrying prohibition. Other Poskim however rule that we do not suspect for this occurrence and it is thus allowed to swim in such a pool from the letter of the law. Nevertheless, even according to them, since today we are accustomed not to bathe even in cold water, and one who swims in the water appears as if he is contradicting the custom [even though in truth he was allowed to enter the water, such as he needed a Mikveh] therefore one is not allowed to do so. Furthermore, if the pool has a depth of ten Tefachim and is four by four Amos wide then seemingly it has the status of a Reshus Hayachid, while outside the pool has a status of a Karmalis, and it hence should be forbidden according to all to enter and leave the pool with the water on one’s body as one is carrying the water from a Reshus Hayachid to a Karmalis.
May one who entered a rimmed pool to immerse in, or to cool off in, swim in that pool?
One who has entered a pool in order to immerse in or to cool off in is not allowed to swim in that pool, even if it is rimmed, as to others it will appear that he is breaking the custom to not bathe in cold water on Shabbos. Furthermore, swimming may involve the same prohibition as does exercising on Shabbos if one intends to swim for exercising purposes. [However it is permitted for him to tread in the pool, and he thus does not have to be careful not to lift his feet while immersing in the pool water.]
May one swim or tread inside a Mikveh?
One is forbidden to do so even if the Mikveh is not filled to its top, unless it has an external rim which will flow back any water that splashes out.
Today one may never swim in a pool or river even in cases that he is allowed to bathe in it even according to the custom, such as to cool off or to do Tevilah.
 Admur 339:1
 Admur ibid and 248:9 regarding the prohibition of entering a ship and 326:6; Michaber 339:2; Mishneh Beitza 36b
Other opinions: Some Poskim suggest that the decree against swimming in pools does not apply at all today being that we no longer make the swimming rafts. [Nodah Beyehuda Tinyana 49 that so would be the law according to Tosafus Beitza 30a regarding clapping on Shabbos] Practically however, this is not agreed upon by all Poskim. [Noda Beyehuda ibid; Ketzos Hashulchan 146 footnote 34:17] Nonetheless, one may use this lenient opinion as joint reason to allow one to splash away twigs in a Mikveh as will be explained in next Halacha.
 Admur ibid and 248:9; Gemara ibid and Rashi ibid; M”B 339:2
 Admur ibid; Michaber ibid; Shabbos 41a as explained by Rashi ibid; Razah; Ramban; Ran
 Admur ibid; Michaber ibid; Shabbos 40b
 Admur ibid; Michaber ibid; Rishonim ibid
 Admur ibid; Michaber ibif; Shabbos ibid
 Ketzos Hashulchan 146 footnote 34 number 16
 Mishneh Berurah 339:2; Ketzos Hashulchan 146:18; Rashi
 Ketzos Hashulchan 146 footnote 34 number 16.
 Ketzos Hashulchan 146 footnote 34 number 13 and 15.
 M”B 339:6
 The Ketzos Hashulchan ibid analyzed this scenario and although leans to be lenient from the letter of the law, he rules that one may not do so being that the scenario is not discussed in the Poskim. The following is the reason to be stringent: Since if this pool were to be filled to the top then the waters would leave the pool, therefore we are stringent to consider them similar to a river. However, by a pool with an external rim it is not common at all to fill the external rim with water, and thus this comparison to a river is not relevant. [Ketzos Hashulchan ibid 13]
 Ketzos Hashulchan 146 footnote 34
 M”B 339:4, based on his understanding of the opinion of Rashi Shabbos ibid and Rambam as he explains in Biur Halacha 339:1 “Veim”; Minchas Yitzchak 6:32
 The reason for forbidding pools is because perhaps the waters will splash past 4 cubits.
 Ketzos Hashulchan 146 footnote 34 based on the opinion of Rif and others [brought in Biur Halacha ibid] which hold the reason for forbidding pools is due to it being similar to a river of which swimming is prohibited, and thus if the pool has a rim it is permitted since it is no longer similar. Furthermore the Ketzos Hashulchan argues on the M”B understanding of Rashi and says that even according to Rashi a rimmed pool is not suspected for splashing out of 4 cubits. He concludes that in any event since the SHU”A clearly rules like the Rif and not Rashi there is no need to suspect for the M”B from the letter of the law.
 Ketzos Hashulchan ibid 16
 Piskeiy Teshuvos 326:7 based on 358, M”B 358:89
 Ketzos Hashulchan 146 footnote 34; Minchas Yitzchak 5:32; Igros Moshe Y.D. 2:13; Beir Moshe 3:56; Shraga Hameir 6:151; Teshuvos Vehanhagos 1:222; Piskeiy Teshuvos 339:1
 Piskeiy Teshuvos 326
 Ketzos Hashulchan 146 footnote 34:17; See also Piskeiy Teshuvos 339:1 footnote 1
 So is implied from Ketzos Hashulchan 146 footnote 34:17 which begins saying that it is forbidden to swim in the Mikveh and then goes on to explain that ideally splashing twigs away is as well forbidden, but the custom of the world is to be lenient in splashing away twigs. He then gives 5 different reasons for why one may be lenient in splashing away the twigs. Now although most of the reasons mentioned apply equally to allowing one to swim in the Mikveh, nevertheless he clearly states that the reasons are to allow splashing away the twigs and not to swim, as well as that some of the reasons only apply to splashing away twigs.