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How does anchor ice form on the bottom of streams?

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ice in lakes and rivers Heat flow through an ice cover (see text).

Anchor ice forms in rivers and streams due to the unique conditions of turbulent, supercooled water. Unlike lakes, the turbulence in rivers mixes the water column, allowing the entire depth to cool uniformly to the freezing point and slightly below, a state known as supercooling.1

During this process, small ice particles called frazil ice form within the flow. Because the water is supercooled, these particles are inherently unstable and actively grow, causing them to stick to one another or to submerged objects upon contact. When these frazil particles adhere to the riverbed, they accumulate into a loose, porous layer known as anchor ice.12

This formation is often temporary; anchor ice frequently develops in shallow streams at night when cooling is most intense, only to be released from the bottom the following day as solar radiation and rising air temperatures warm the water slightly above the freezing point.1