Frazil ice begins forming when turbulent, open water becomes super-cooled (i.e., water temperatures reach 0 degrees Celsius, or colder) normally when wind chills drop below minus 18C. Frazil ice is characterized as fine particles of ice suspended in the flowing water and resembles slush. These particles can build up very rapidly as they are extremely sticky and easily adhere to objects in the water, including the underside of an ice sheet or the river bottom. Anchor ice is frazil ice that is attached or anchored to the river bottom. As these particles build, they may result in a dam, (often not visible from the surface) which may reduce the capacity and the direction of the water flow, resulting in flooding.
Areas which have experienced this phenomenon in the past include, but are not limited to, Clyde River, Fall River, Indian River, Mississippi River at Snow Road, Sheridan Rapids, Playfairville, Ferguson Falls, Innisville, Appleton, Almonte, Blakeney and Pakenham.