Properly speaking, this is not an oasis but a small, reedy lake. Nanhu means South Lake in the language of the nomads. Because wells are widely scattered in this region, Nanhu is an important watering place for the nomads and the few caravans that go by the northern route of the silk road through the Fergana pass.
Nanhu is a small lake, very shallow and choked with reeds. During summers, it occasionally dries up, leaving nothing but crusted mud on the surface. The nomads know that by digging beneath the surface, they can usually find water. Because of its erratic water supply, however, no one has settled near the lake.
During summertime there, is a 25% chance the lake will be dry, unless there has been a recent rain. If the surface is dry, a second check (also 25%) should be made to see if the water table under the crust has also drained away. Otherwise, characters who dig will be able to find enough muddy water for themselves and their mounts.
The oasis is also the home of an ubbe. During times when the lake is dry, the ubbe hibernates in the mud below the surface. The creature releases its captives at this time, thus this ubbe is not considered as evil or vicious as others.