The Changyuan River was a river on the border between Qing State and Yu State. It flowed through the territories of both states, but its current wasn't particularly strong. During the dry season, it would even run dry.
The river had dried up during the great drought that previously struck Qing State, but this year, its flow was considerable.
The Changyuan River wasn't far from Tan City, which Yang Chan had visited before. That was where he had dealt with the members of the No-Life Evil Cult who came from Yu State.
Naturally, Yang Chan had returned to this area.
He chose the Changyuan River precisely because he had been here before.
The Qingyuan River would have actually been a better choice, but due to Taiyin Heaven, the Spiritual Qi in the vicinity had surged, attracting many people and potentially causing trouble.
So, Yang Chan didn't choose the Qingyuan River. Instead, he opted for the more remote Changyuan River to save himself a lot of hassle.
