Commentaire sur Shabbat 11:4

הזורק בים – from the beginning of four [cubits] to the end of four [cubits], he is exempt, for it is a Karmelit.

Introduction This mishnah deals with throwing in bodies of water.

רקק מים – which are not higher from the land, and there is in them mud and clay/plaster and they are called a [shallow] pool/diluvium.

If one throws in the sea four cubits, he is exempt. The sea is considered a “karmelit”, a place which is neither a public nor a private domain. That means that one is not liable for carrying or throwing in the sea.

ור"ה מהלכת בו – for many [people] walk through it.

If there is a pool of water and a public road crosses it, and one throws [an object] four cubits in it, he is liable. And how deep is a pool of water? Less than ten handbreadths. [For] if there is a pool of water and a public road crosses it, and one throws [an object] four cubits in it, he is liable. This section deals with a pool of water that lies in the public domain. If, the pool of water is less than ten handbreadths deep then one who throws an object four cubits into it is liable. The reason is that if it is less than ten handbreadths, then it is considered to be part of the public domain and one who throws or carries in it is liable. However, if the pool of water is more than ten handbreadths deep then it is no longer considered to be the public domain and one who throws in it she is exempt. We should note that the Talmud questions why section two seems to repeat itself at the end. From this repetition the talmud derives additional laws.

וכמה הוא רקק – what is its depth that we can say that it is yet the public domain and it has not become a Karmelit?

ורקק מים ורה"ר מהלכת בו – this is double that was taught for the matter to teach us that even if the pool was four [cubits] wide, for since it was less than ten [cubits] high, it is judged like the public domain, and double also with a public domain going through it to teach us that even though many people don’t walk through it other than in an emergency/need, walking even in an emergency is called walking.