A. Tashlich-Where to say it:
It is customary to go on Rosh Hashanah to a river [or well or spring] to recite Tashlich. Tashlich is to be recited near a river that contains live fish. [See Q&A regarding if a river is not available.] It is best to be recited near a river that is outside the city [but within the Techum].
Q&A on where to recite
What is one to do if a river, well or spring is not available in one’s city?
In a case that a river, well, or spring is not available in one’s area, then some are accustomed to walk to an area from which they can see a river, sea or other body of water, even if it is very far. In Yerushalayim, some were accustomed to recite Tashlich near the opening of a water pit, even if it is currently dry of water. If this too is not available then one may go to any body of water, even an open faucet.
Q&A on fish
May one feed the fish by the river?
No. It is forbidden to feed fish on Yom Tov [unless they are in an aquarium and dependent on humans for their food].
The Rebbe’s Tashlich:
For an accounting of the Rebbe’s Tashlich see Otzer Minhagei Chabad P. 351. In the earlier years the Rebbe went to the Botanical gardens; One year there was a lot of rain; the Rebbe once climbed the fence to get to the lake; Starting from 1968 a pond was built in the courtyard of 770
B. Who-Are women to say Tashlich?
Many women are accustomed to reciting Tashlich. Nevertheless they are not to go to an area where there are men as this can lead to promiscuity and sin. Some Poskim denounce the custom of women saying Tashlich due to this reason.
 Admur 583:7; However, in the Rama ibid and Siddur it simply states that one goes. The Shlah [Miseches R”H 214b in gloss] states that this is an old custom.
The Sefaradi custom: Although this custom is sourced in the Ashkenazi Poskim, nevertheless it is followed also by Sefaradim. [so is proven from all the Sefardi Poskim mentioned in the footnotes here that discuss the details of the custom of Tashlich]
Custom of Gr”a and others: In Maaseh Rav 209 it states that the Gr”a was not accustomed to go near a body of water to recite Tashlich. The Aruch Hashulchan 583:4 records that many are accustomed not to perform Tashlich at all for reasons known to them and he concludes “and so is proper”.
 Admur 583:7 [“river” is omitted in Siddur]; Rama ibid; Mahril ibid; M”A 583:5 and Shaar Hakavanos 90b mention both options, a river or well. Vetzrauch Iyun on why Admur omitted this from the Siddur.
 Siddur Admur; [omitted from 583:7]; M”A 583:5; Shaar Hakavanos 90b; Peri Eitz Chaim 26:5; Mishnes Chassidim 9:14; Kaf Hachaim 583:30
 Source of the word Tashlich: The word Tashlich means to throw and represents the throwing of the sins. [see Sparks of Kabala]
 Admur 583:7; Darkei Moshe 583:2; Drashos Mahril; Minhagim; Shlah 214b; M”B 583:8; Kitzur SHU”A 129:21
The ruling in Siddur: Admur in the Siddur does not explicitly write that the water should contain fish. Veztaruch iyun. See glosses of Rav Raskin p. 538.
The significance of fish: The fish serve as an omen that the evil eye should not have authority over us. It is also an omen for us to be blessed to multiply like fish. [Admur ibid; Minhagim; Darkei Moshe 583:2] Alternatively, the reason is because we are a parable to live fish that have been suddenly caught in a net and we beg for supplication of mercy. [Mateh Moshe 820; Shlah 214b] Alternatively the fish represent the level of “Eina Pikcha” [Siddur Admur; Shlah 214b; see Kitzur SHU”A 129:21 where all the reasons are brought] The seeing of fish by the river is secondary to the main purpose of Tashlich. [So is evident from wording in Shlah p. 214 “and consequently one also sees fish”]
Other Poskim: The Rama ibid omits the necessity of having fish in the waters. It is likewise omitted from the Kisvei Arizal brought in footnotes.
 Siddur Admur; Admur 583:7; M”A 583:5; Elya Raba 596:3; Siddur Yaavetz; M”B 583:8
 Custom of Chasam Sofer recorded in Piskeiy Teshuvos 583 footnote 47
 Kaf Hachaim 583:30
The reason: As the main intent of Tashlich is with regards to the supernal sea, and the water below is merely a hint to this matter. [ibid]
 Nitei Gavriel 69:6 and so is the custom of many communities in Israel; Directive of Rebbe to Rav Yaakov Yehuda Hecht [Hiskashrus 947]
 Admur 324:7; Mateh Efraim 598:5; Kaf Hachaim 583:32
 Zechor Leavraham 583 brought in Piskeiy Teshuvos 583 footnote 51
 Aruch Hashulchan 583:4 states that women should not go and in an area that women go then the men are not to go; Alef Hamagen 583:7