First of all, a comment on swimming in general: the obligation of exercising caution – “You shall guard your lives carefully” – requires that we avoid situations of danger. Hence, a person should not swim in the sea in a place where there is no lifeguard, and likewise, wherever else he swims, he should ensure that he is safe.

Rav Neuwirth, in his Shemirat Shabbat ke-Hilkhata (chapter 14, par. 12) writes: “It is forbidden to swim on Shabbat as well as on Yom Tov; it is likewise customary not to bathe either in the sea or in a pool, even without swimming.”

The nature of Shabbat requires that we dedicate the day to God, spending our time in spiritual pursuits together with the family. This is our guiding principle for all rulings concerning the laws of Shabbat.

Beyond the question of the nature and spirit of Shabbat, swimming on Shabbat may entail the following problems:

•   Wringing: this is a Torah prohibition on Shabbat, derived from the category of activity known as treading (‘dash’). Swimming may lead us to wringing the bathing costume or towel, or squeezing hair with the towel to dry it.

•   Where there is no ‘eruv’, there is also a problem of carrying. This prohibition includes both objects that the person is carrying and the water upon his body that he takes with him when he comes out of the pool.

•   In a heated pool there are two further problems (Shulhan Arukh, Orah Haim siman 326):

    1. Bathing in warm water that has been heated on Shabbat. Heating water on Shabbat is prohibited under the category of cooking.

   2. The Sages instituted a prohibition against bathing the entire body on Shabbat even using water that was heated on Friday, so as to avoid the possibility of water being heated on Shabbat for the purposes of bathing on Shabbat.

•   “We do not float (Mishna Berura: that one’s feet are lifted from the floor of the water) on the surface of the water (Mishna Beitza, chapter 5, mishna 2), lest a person come to fashion for himself a barrel upon which to sail” (an object used while learning to swim – like water-wings or a swimming ring today). This rabbinical enactment applies specifically to rivers that have no edge to hold on to, and whose floor is sand; not to a swimming pool.

•   Fast or prolonged swimming that is undertaken for the purposes of physical fitness is prohibited like any other exercise for that purpose: “We do not exercise – i.e., exerting oneself in order that he will work [his muscles] and perspire” (Shulhan Arukh, Orah Haim, siman 328, par. 42).

Since there are so many different ways in which a person may inadvertently end up transgressing the laws of Shabbat, later halakhic authorities have ruled that one may not swim in a pool on Shabbat.