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. period with harsh winter weather conditions, a situation 

 occurring in Montana, increases the severity of the stream 

 environment in winter. 



Winter flow depletions will expose a greater area of the 

 stream bed to radiant heat loss, thereby increasing the 

 likelihood the stream will supercool and form anchor ice. 

 Because flows are already at their lowest natural levels in 

 winter, even small depletions can greatly increase the 

 amount of exposed stream bed. The volume of water in a 

 stream channel alone may provide some insulation against 

 heat loss, slowing down the supercooling process and in turn 

 the formation of anchor ice. When anchor ice does form, 

 obliterating some stream habitats and alternately flooding 

 and dewatering others, the maintenance of the normal stream 

 flow likely benefits fish by providing greater survival 

 space. Mortalities caused by catastropic weather events 

 will be even greater if the escape space is reduced, an 

 event likely to result when winter flows are depleted. 

 Total stream freeze-up is also possible given sufficient 

 winter depletions. Such an event occurred in Rattlesnake 

 Creek, Montana, following winter flow reductions (D. 

 Workman, per. comm.). 



In winter the primary concern in regard to food production 

 is to maintain enough wetted habitat to overwinter the 

 immature stages of the semi-aquatic insects that serve as 



