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Anchor ice in particular can be very destructive to trout 

 and other aquatic life (Butler, 1979). During nights when 

 clear skies provide maximum radiant heat loss from the land 

 and water and air temperatures are low enough to supercool 

 the stream, small ice crystals, called frazil ice, form in 

 the water. The frazil ice drifts downstream and attaches to 

 the first object in its path, accumulates and forms a mat of 

 anchor ice over the bottom. Frazil ice alone can be harmful 

 to fish by plugging their mouths and gills, resulting in 

 suffocation. Tack (1938) reported such a fish kill in trout 

 ponds. ^ 



As the anchor ice accumulates, ice dams are built up in 

 various sections of the stream. As the ice mass builds, the 

 stream becomes elevated and is forced out of its bed, 

 becoming impounded in areas frequently flooded in the 

 spring. Areas habitually used by fish can be obliterated by 

 the ice, causing fish to lose their orientation and swim 

 aimlessly through the ice caverns. As heat from the sun is 

 absorbed during the day, the anchor ice and ice dams melt 

 and the stream quickly returns to its former bed, stranding 

 fish and other aquatic organisms in the overflow areas. 

 This sequence can be repeated night after night if 

 conditions are right. 



Heavy snow cover on the ground, streambanks and tops of 

 instream boulders insulates against radiant heat loss and 



