to allow assessment of the impacts of lowered streamflow on fish populations. 

 The reconmended minimum passage and spawning flow for sauger from March through 

 June is 14.9 m^/sec. For shovelnose sturgeon, the reconmended flow for passage 

 and spawning for May, June, and half of July is 17 m^/sec. Channel catfish 

 spawn in the Tongue River in June, July, and August; the recommended flow 

 for this species is 6.4 m^/sec. For the remainder of the year, it is 

 reconmended that rearing flows of 5 m^/sec (the reconmended flow for rearing 

 of stonecats) be maintained. 



It is the naturally occurring flow regime, including low flows, that has 

 resulted in the existing aquatic biota of the Tongue River. That naturally 

 occurring pattern of low flows is described in this report and compared with 

 the predicted flows after each of three future levels of development. Compari- 

 son of the predicted post-development low flows at the mouth of the river with 

 the reconmended passage and spawning flows given above shows that even for the 

 low level of development, fall flows would not supply the recommended channel 

 catfish spawning flow. Lowered flows resulting from the intermediate level 

 of development would have a severe impact on all indicator fish species. At 

 the high level of development, flows would be almost nonexistent downstream 

 from the T&Y Diversion, and impacts on the fishery would be extreme. Water 

 quality would also be affected by agricultural and industrial development 

 and water use in the Tongue River Basin, with some adverse effect on the 

 fishery. The potential alteration of other limiting factors, such as 

 temperature, pollution, and turbidity, among others, is also discussed. 



76 



