(Excerpted from MBY Archives, The 39 Melachos, by Rabbi Ribiat (Vol. IV) and Mishnah Torah by Rambam (Laws of Shabbos, Chap. 23)
1) No riding an animal
(Excerpted from MBY 305:18-20 Allowing one’s animal to rest - part 3)
Question: Is it permissible to ride an animal (e.g. horse or donkey) on Shabbos?
Answer: (I’m afraid there is a lot riding on my answer!) No, it is not permissible.
The rabbis made a decree forbidding the riding of an animal on Shabbos. Their (stated) main concern was that the rider would inadvertently transgress the act of ‘toleish’ – uprooting (i.e. pulling a branch off of a tree to use as a whip or goad with which to drive the animal). The decree was unequivocal (Heb: ‘lo plug’ – no differentiation), i.e. it applied even in places such as deserts where there were no trees to be found. In addition, the rabbis extended their decree to include any kind of leaning on or using the back of animals - even to sit on a wagon which was being pulled by an animal!
2) WARNING: No Swimming Allowed!
(Excerpted from The 39 Melachos, by Rabbi Ribiat, Vol. IV, pp. 1190-1191) Swimming on Shabbos. Swimming in a river or pond on Shabbos or Yom Tov is forbidden by Rabbinical ordinance, because swimming could lead to ‘makeh b’patish’ (lit. ‘the final hammer blow’, i.e. the melacha against completing or fixing a vessel.) The reason for this Rabbinic ordinance. In the period of the Talmud, swimming was taught with the aid of a type of life-preserver made of bulrushes or reeds. The reeds were woven into a barrel-shaped float that was completely enclosed and air-tight. This buoyant device served much the same purpose as a modern life-preserver. The Talmud refers to this float as a ‘chavis shel shayatin’ – lit. a swimmer’s barrel. (According to some commentaries, the barrel referred to by the Talmud not made of reeds, but was actually a hollow earthenware vessel shaped like a barrel…) Apparently, these floats would frequently become damaged or punctured and lose their buoyancy. (Ed: OH BUOY!) It also seems that repairing them was something that most people could do rather easily. However, even a simple, minor repair would be the forbidden melacha mid’oraisa (Torah-prohibition) of ‘makeh b’patish’. Because Chazal understood that persons engrossed in swimming activities were likely to forget themselves, and on the spur of the moment, make a quick and simple repair on a life-preserver, they imposed a strict ordinance forbidding swimming on Shabbos and Yom Tov. Swimming today. The prohibition on swimming in a river or pond extends to all situations, i.e. even when there is little or no likelihood that this could lead to any type of repairs. Rabbinic ordinances are generally categorical, i.e. applying even in times and conditions where the original considerations and reasons for the ordinance do not exist. Therefore, swimming is forbidden even in modern times when the early-day type of life-preserver is no longer ever used.
Swimming in a swimming pool. There is technically some Halachic basis to distinguish between a river and a swimming pool, thereby permitting swimming in certain pools. However, not all pools could be permitted. Moreover, even in cases where the specific Rabbinic ordinance against swimming could be circumvented, any leniency is not very practical for at least two reasons:
a. Swimming will cause the swimming garments to become wet, thereby transgressing the melacha of ‘melabain’ (laundering)
b. Even if one could contrive a non-absorbent swimming outfit (e.g. plastic, vinyl, etc.), there is nevertheless a widely-held custom not to immerse (i.e. bathe) in even cold water for any other purpose than for a mitzvah.
Floating objects in a pond. Included under the restriction on swimming is a prohibition on the act of floating objects, e.g. toy boats, logs, etc., in a river or pond. Therefore, persons vacationing in a bungalow colony or summer camp should be aware that it is forbidden to place floating objects into a pond on Shabbos (even where there is an Eruv) or Yom Tov.
3) No mitzvah “transactions”
(Excerpted from Rambam’s Hilchos Shabbos, Chap. 23:15, Moznaim translated edition) Jewish Court (Beis Din) is not convened on Shabbos, nor are the rites of chalitza (Footnote #66: the ceremony through which a childless widow frees her brother-in-law from the obligation of yibum – see below) or yibum (Footnote #67: This refers to the rite in which the brother-in-law of a childless widow marries her in order to perpetuate the name of her dead husband - see Devarim 25:5-10) conducted, nor are women betrothed (Why? - ) lest one write. Property may not be consecrated, nor may endowment evaluations be made, nor may property be set aside (e.g. for leins), because this resembles a sale. Nor may teruma and ma’aser tithes be separated, for this resembles consecrating the produce one has separated, and also because, through this ritual, one makes the produce fit for use on Shabbos. One may not tithe one’s animals either. This is a decree instituted lest one mark the animal with red paint (i.e. a rite used to identify the tenth in a series, which would be used as a korban/offering.) A person may, however, consecrate his Pesach sacrifice on Shabbos and his festival offering on a holiday, for this is the mitzvah associated with that day. Just as property may not be consecrated, so too, water may not be consecrated for use in sprinkling the ashes of the Red Heifer.