The river Styx is a permanent conduit through the lower planes, from the battlefields of Acheron through the Nine Hells, Gehenna, Hades, Tarterus, the Abyss, and Pandemonium. It functions in much the same way as the Yggdrasil as a method of transportation through these planes. Contrary to speculation, the Styx does not extend into the Astral plane, though portals do stand on the banks of the river, enabling the boatmen of that fell river to reach the Astral plane.
The Styx is always in motion as it flows through the top layers of each of the seven lower planes. The fifth level of the Nine Hells, which contains the world-ocean Stygia, is connected to the Styx, as are a number of the deeper layers of the Abyss. The Styx does not appear to have a origin or a final outflow, nor does it move linearly to adjacent planes. Boatmen have been able to pass from Acheron to the Abyss in a matter of hours, without passing through the planes between them. The tangled skein that is the full flow of the Styx has not been measured. Perhaps it cannot be measured, seeing as it is an infinitely long river that passes through a number of infinite planes.
Those who touch, drink, or are immersed in the Styx forget their entire past life, including spells and all alignments save their original one. A saving throw vs. spell is applicabl. Those who are immersed in the river have the standard chance of drowning in the swift flow. There is also a 50% chance of being dragged into another plane before reaching the shore.
The same holds for boats, in addition to a 20% chance of overturning for small craft and a 10% chance for large vessels. Nonnative travelers boating upon the Styx, or those attempting to water walk or fly across it have a 40% chance of attracting the attention of 5d6 hydrodaemons or 3d4 styx devils (the latter if in the Nine Hells). Most travelers on the Styx rely instead on the native boatmen of the planes, Charon and the charonadaemons. Charon can take the travelers anywhere on the Styx, as well as into the Astral, Ethereal or Prime planes. Transit time is 1d100 turns.
Normal encounters apply, and in these encounters Charon does not interfere unless his boat is threatened. Charonadaemons are lesser daemons who work in the service of Charon as boatmen. They share his knowledge of the Styx, the Astral, the Ethereal, and the various Prime planes. The time for transit by charonadaemon is longer, 1d10 days, and normal encounters occur. Like Charon, the charonadaemons do not attack or interfere with party actions. There is a 10% chance per day of travel with a charonadaemon that the boat picks up other travelers (who are native to the current plane and probably hostile to the party). Charon, if hired, does not stop for other passengers.