Styx has always been dear to Zeus because she was the first to step forth (with her numerious children) and promise to fight for Zeus against all his enemies.
She is a mighty river and her power helped Zeus gain victory over the elder gods and secure his throne on Olympos.
Any immortal who pours the waters of Styx, and swears an oath, is solemnly bound to tell only the truth. The punishment for breaking such an oath is one year without ambrosia, nectar or AIR! If that’s not enough, for nine additional years, the oath-breaker is not allowed to attend the festivals or share the company of the other immortals.
This Fun Fact was taken from Theogony (793).