Swallow River has two sources, the south source is Lin 'an River and Wainan River, which originated in three provinces and Tiantangzhai Mountain range in Dabie Mountain. The northern source is Huanghe River, which originates from Mazongling, the northern branch of Sanxian Mountain in the three provinces, and the two sources meet at Dashi River. Downstream, Yanzi River is called Dashi River, Changtan River, Lvzhu River, Qilin River, Taer River and Maotan River in turn, and flows into xianghongdian reservoir. Swallow River flows downstream, and several small tributaries and streams keep flowing in.
The Yanzi River Alpine Canyon is navigable because of its large gap, but it is rich in hydropower resources. There are two small reservoirs: Dongfeng Reservoir in the upper reaches of Dashi River (1968, storage capacity180,000 cubic meters) and Wendian Reservoir in Ta 'er River (1968, storage capacity195,000 cubic meters). The main dike project is the stone revetment of Dashihe River, which is 5 kilometers long. There are 10 small hydropower stations with a total installed capacity of10 million kilowatts.