Maybe it isn’t customary because in Bnei Brak, Yeruham, and Lod there is no sea.
But saying Nishmat Kol Chai early on Sabbath morning in Akko by the sea, from experience, is absolutely awe-inspiring, almost frightening at the level of the idea itself
so maybe that does count as an accepted practice?

Looks to me like it’s permitted and even a commandment,
because Sabbath is an acronym:
Sabbath — Delight in the Sea.

What is the law regarding a swimming pool in a private domain?

Apply my answer above.

Regarding carrying water in a karmelit and the need to dry off, I got the following response from ChatGPT:

The Shulchan Arukh (Orach Chayim 301:2) rules that water on a person’s body is secondary to him and is not defined as a separate object.

The Mishnah Berurah there (subsection 13) explains that this is similar to mud on one’s feet or dust on one’s clothes — they are subordinate to the person and are not considered something one is “carrying” in their own right.

As long as the water is on the skin in a natural way (it stuck there after washing), it is part of your body for purposes of this law.

Oren, you’re a much bigger expert than I am in AI, and you’re surely familiar with the phenomenon of hallucinations. It turns out they still exist in GPT-5 too.

In the AI’s defense, I used the regular 5 model and not 5 thinking. But in any case, the reasoning it hallucinated sounds correct to me. I also thought it’s no different from rain, where water droplets also stick to your body and you carry them around, and nobody forbids that kind of carrying. In other words, I’m asking why it should be forbidden to carry sea water that stuck to the body, in light of the AI’s reasoning and the comparison to rain.

There is a difference between droplets that are on the body and water that you want to remove or dry off. If in the first case it may be considered secondary, in the second case perhaps not.

By the way, does the thinking model hallucinate less, or does it just think better?

Both, in my ungrounded opinion.

As for droplets on the body, even in the case of heavy rain I need to dry myself off. Also, if there were a problem with carrying water stuck to the body in the sea on the Sabbath, then entering the sea should have to be completely forbidden, because there is no way not to carry the water, since it is impossible to carry a towel for the sake of drying off.

Anything you want to dry off is not secondary, in my opinion. And of course, if there is a problem with the towel, then it is forbidden.

So according to that, someone who gets very wet in heavy rain and wants to dry off because of all the wetness has to stand in place?

In principle, yes. One could discuss the status of someone acting without awareness and without intent.

By the way, in an older responsum you wrote differently:

Excellent question. There is a difference — beyond the amount of water, which is also different — in that at the sea I bring the water up onto myself, whereas in rain it happens to me from outside. But in truth I do not see a logical basis for distinguishing.

Those are exactly the two arguments I brought. And still, logically, there is no distinction. If this were in a public domain, where the prohibition is Torah-level, would we permit it there too because there is no choice? Let him stand in place; “there is no wisdom and no understanding and no counsel against the Lord.” And bringing the water out of the river or the sea is also something he does not want. These arguments are extremely weak.

See this link:
https://mikyab.net/%D7%A9%D7%95%D7%AA/%D7%98%D7%9C%D7%98%D7%95%D7%9C-%D7%9E%D7%99%D7%9D-%D7%91%D7%A9%D7%91%D7%AA/

I didn’t see what is different there.

I thought about this again, and it reminded me of what you said about yeshiva heads who have no contact with ordinary householders who can tell them that a certain halakhic ruling of theirs makes no plain sense — unlike yeshiva students. Here too, it seems to me impossible that someone who gets very wet in heavy rain and keeps walking despite that is doing some transgression or some prohibited labor on the Sabbath. It’s simply against common sense. It may be that when you analyze the sources and try to compare one case to another, that is what comes out, but the final result seems very strange to me.

Possibly. Still, that kind of intuition can be a motivation to look for a halakhic explanation. But to permit it, one has to find a halakhic explanation. You might perhaps say that as long as I am in a public domain and have no option to dry off the liquid from myself, then it is indeed secondary. Or that the rain fell on me and there is no act of lifting here, only at most placing down, unlike with sea water. Also, these are liquids that I do not want.

Following up on this responsum: regarding the problem of carrying the water on the Sabbath, does that problem also exist on a strip of beach belonging to a certain hotel at the Dead Sea?

A karmelit can be privately owned just as a private domain can belong to the public. For purposes of Sabbath domains, ownership is not what determines the status, but the form and size of the place. Anything that is neither a public domain nor a private domain is a karmelit.