How does supercooling lead to the formation of frazil ice in rivers?

In rivers, turbulent mixing causes the entire water column to cool uniformly. When the water temperature drops below the freezing point, a state known as supercooling occurs.1

During this process, the introduction of ice particles from the air triggers nucleation, leading to the formation of frazil ice—small, disk-shaped ice particles typically 1 millimeter or smaller in size. This freezing action releases latent heat, which helps return the water temperature toward the freezing point.1

Supercooling is essential for the growth and behavior of these particles. Because the water is supercooled, frazil ice particles are inherently unstable and actively grow. This condition allows them to stick to one another or to other surfaces upon contact, causing them to freeze together into larger masses, slushlike formations, or anchor ice on the riverbed. If the water temperature rises above the freezing point, the particles become neutral and lose their ability to adhere to one another.1