The River Styx is mentioned quite a lot when a Greek hero meets his demise.
However is this really a body of water in Hades?
Is it made out of something else?
What is the River Styx?
Once the war was won, Zeus, king of the Olympians, promised that every oath be sworn on Styx's name, as a sign of the greatest respect.
He also proceeded to name the River Styx after her.
Achilles was dipped in it as a child and was rewarded with invulnerability, except for his heel, which was where his mother was holding him, hence the term : Achilles' heel.
The full list of rivers surrounding Hades :
It is the mystical division between life and death - or rather, life and afterlife. It is a symbol of that border.
It is definitely not made out of normal water, as falling into the Styx causes one to lose one's memories. Which is why one has to take the ferry to the other side.