Tashlich (תשליך) is a ritual that many Jews observe during Rosh HaShanah. "Tashlich" means "casting off" in Hebrew and involves symbolically casting off the sins of the previous year by tossing pieces of bread or another food into a body of flowing water. Just as the water carries away the bits of bread, so too are sins symbolically carried away. In this way the participant hopes to start the New Year with a clean slate.
The Origin of Tashlich
Tashlich originated during the Middle Ages and was inspired by a verse uttered by the prophet Micah:
God will take us back in love;
God will cover up our iniquites,
You [God] will hurl all our sins
Into the depths of the sea. (Micah 7:19)
As the custom evolved it became tradition to go to a river and symbolically cast your sins into the water on the first day of Rosh HaShanah.
How to Observe Tashlich
Tashlich is traditionally performed on the first day of Rosh HaShanah, but if this day falls on Shabbat then tashlich isn't observed until the second day of Rosh HaShanah. If it is not performed on the first day of Rosh HaShanah it can be done anytime up until the last day of Sukkot, which is thought to be the last day of the New Year's "judgment" period.
In order to perform tashlich take pieces of bread or another food and go to a flowing body of water such as a river, stream, sea or ocean. Lakes or ponds that have fish are also a good place, both because the animals will eat the food and because fish are immune to the evil eye. Some traditions say that fish are also significant because they can be trapped in nets just as we can be trapped in sin.
Recite the following blessing from Micah 7:18-20 and then toss the bits of bread into the water:
Who is like You, God, who removes iniquity and overlooks transgression of the remainder of His inheritance. He does not remain angry forever because He desires kindness. He will return and He will be merciful to us, and He will conquer our iniquities, and He will cast off our sins into the depths of the seas. Give truth to Jacob, kindness to Abraham, like that you swore to our ancestors from long ago.
In some communities people will also pull out their pockets and shake them to make sure any lingering sins are cast off.
Tashlich has traditionally been a solemn ceremony but in recent years it has become a very social mitzvah. People will often gather at the same body of water to perform the ritual, then they'll catch up with friends they haven't seen in a while afterward. In New York, for example, it is popular to perform tashlich by tossing pieces of bread off the Brooklyn or Manhattan bridges.