It was scorching hot this past Shabbat, and we were wondering if we were allowed to go swimming in the nearby lake to cool ourselves off. What is the halachah?

Answer

There are various potential issues with swimming on Shabbat. But, as with many areas of halachah, context and precise definitions matter. So let’s dive in.

Rivers, Lakes and Ponds

The Mishnah states that one may not go swimming on Shabbat,1 which is defined as lifting both feet from the ground and floating or treading water.2 The Talmud explains that the reason for this decree was because swimming could lead to building some sort of flotation device (perhaps to help someone learn to swim), which is prohibited on Shabbat.3

However, this prohibition only applies to swimming in a body of water similar to a lake or pond. This also includes a man-made pool of water, if, when one swims in it, he is likely to slosh out some water, which will then run into rivulets and pools, resembling (to some degree) a pond or lake. If, however, you were to fill a large receptacle (such as a tub) with water, then this particular prohibition would not apply, since it is uncommon to make a flotation device for a receptacle. This would also include an in-ground pool with a rim around it, which prevents the water from sloshing outside.4

This ruling has led to a debate regarding contemporary pools. Although they usually don’t have a rim around them, they aren’t filled to the top, which prevents the water from splashing out. Are these pools considered “rimmed” or “unrimmed”?5

As we’ll see, there are other concerns with swimming that render the discussion of contemporary pools largely moot.

Peripheral Issues: Bathing Suits and Carrying

Assuming you would be wearing a bathing suit, there is the potential to violate the prohibition of sechitah (squeezing out water).6 Additionally, if you were to swim outside of an eruv, leaving the pool could also potentially be an issue of carrying the water in a public domain.7

Dunking on Shabbat

Even if you were to avoid the above prohibitions, the accepted custom8 is not to bathe (even in cold water) on Shabbat.9 This would, of course, preclude swimming in all scenarios.10

Nevertheless, if it is for a mitzvah (such as going to the mikvah) or in a situation where it is extremely hot, you would be allowed to dunk in even a rimless (cold-water) pool—without swimming—provided that precaution is taken against the concerns outlined above, such as squeezing or carrying.11

Additionally, if you were medically required to swim on Shabbat, then, with consultation with your rabbi, you would be allowed to do so in a private pool, taking the above precautions.