The River of Tuoni (Finnish: Tuonen joki or Tuonelan virta) is a river that seperates the world of the living from Tuonela. Dead people must cross the dangerous river to get to Tuonela. The river can be either peaceful and dreary, or a "burning" rapid, gigantic whirpool kinahmi. The peaceful river appears in Kalevala.
Tuonen tytti ferries the deceased over the slowly flowing river on her ferryboat. Some living people might also try to get ferried by claiming to be dead. One can also cross the river by swimming, for example if they shift their shape to an aquatic animal. However, there are iron nets in the river and Tuonela has guards. Going to Tuonela is very risky, and it's been told that while many have gone there, only a few have actually survived back.
There is the Swan of Tuoni swimming in the river. Lemminkäinen was killed and thrown into the river when he tried to kill the swan. However, Lemminkäinen's mother picked his son from the river and brought him back to life.
If the river was a rapid, there can be edged weapons flowing in it: swords of men, battle axes of warriors, and needles of women.