The Nan Shan River is a small body of water located in the southern Earth Kingdom that empties into the South Sea. Though the current is strong in some places, in other places the water forms calm pools and streams ideal for bathing or, in Team Avatar's case, washing a sky bison. A duel between Katara, Sokka, Mai, and Ty Lee took place by the river.
Upon arriving at this river, Toph stated that the trail of shedding fur Appa was leaving allowed for Princess Azula and her allies to easily track them down. After a quarrel with Aang and Katara, the earthbender angrily gathered her belongings and left the group to clean Appa themselves. Aang and Katara used their waterbending to wash Appa as Sokka stood knee-deep in the river, brushing out the bison's coat. After Appa's bath, Aang took some of his fur and scattered it around, creating a fake trail in hopes of diverting Princess Azula. The river, however, was filled with clumps of Appa's fur, and the bison had broken several tree tops next to the river during his takeoff, enabling Azula to see through their charade.
While Azula followed Aang's trail to the deserted town of Tu Zin, Mai and Ty Lee pursued Appa, Katara, and Sokka up the Nan Shan River. The exhausted threesome tried their best to outrun the two girls on their mongoose lizards. After Appa managed to cross the river and crash-land on the other side, the Water Tribe siblings momentarily rejoiced, convinced they were safe. However, Azula's allies easily forded the river on their mounts and began to fight. Mai was able to pin Katara to a tree and Ty Lee easily paralyzed Sokka using her chi blocking. As Mai prepared to finish the fight, Appa interfered and airbent the Fire Nation girls into the river with his tail. Both girls were washed ashore downstream.