Why does rime fog form along the Sungari River near Jilin city in winter?

The formation of rime fog along the Sungari River near Jilin city is a unique phenomenon driven by the operation of the Fengman Dam.1

While the region experiences cold winters that typically cause rivers to freeze for several months, the water released from the Fengman hydropower station remains unfrozen throughout the winter. This relatively warmer water, when exposed to the frigid winter air, creates fog containing supercooled water droplets. When these droplets come into contact with surfaces—such as trees along the riverbank—that are at temperatures below the freezing point, they freeze almost immediately upon contact. This process results in the accumulation of rime, a white, opaque, and granular deposit of ice crystals that creates a distinctive and popular winter landscape.2314