river bottom with a resultant loss of habitat and a dramatic decrease in 

 fauna. 



The effects of reduced current velocity and of loss of bottom habitat 

 are separable in their effect of fauna. Reduced current velocities (due to 

 lowered streamflow) could adversely affect bottom fauna even before a 

 significant loss in bottom habitat occurred. Because of the shape of the 

 Yellowstone River channel, flow reductions would result in corresponding 

 reductions in water velocity. For each 1 ,000-cfs reduction in mean low 

 summer discharge in the lower Yellowstone, the aquatic invertebrate population 

 would be reduced by approximately ten percent because of reduced velocity. 

 Further reduction in invertebrate populations could result from other factors 

 related to reduced flow, such as exposure of bottom habitat, increased 

 freezing of the river bottom, and silt accumulation. 



104 



