Nagashi-bina (流し雛)
Nagashi-bina (paper dolls floated downriver) is an event which is said to be the origin of the Dolls' Festival.
It is also called 'hina-nagashi.'
This ceremony is still held in various regions as a folk custom which represents the removal of participants' impurities by throwing them into a river, in the same way as harai-hitogata (purification with a paper doll).
Origin
It has such a long history that appears in the Chapter of Suma in the 'Genji Monogatari' (the Tale of Genji). The story is that Hikaru Genji put a purified hitogata (also called katashiro, which is a paper doll used in Shinto purification rites) on a boat and washed it out to the sea of Suma.