Lower Clark Fork 



Routinely low nutrient concentrations in the Flathead 

 River are responsible for an average 40 to 50 percent 

 reduction in nitrogen and phosphorus concentrations in the 

 lower Clark Fork. Concentrations of total phosphorus (Figure 

 3-28) and total inorganic nitrogen gradually decline toward 

 the Idaho border, and many measurements are at or near the 

 analytical detection limits. Throughout the reach, the total 

 phosphorus criterion is only infrequently exceeded (in 15 

 percent of the samples in FY 86; never exceeded in FY 85 or 

 FY 87) , and the nitrogen criteria are never approached. 



Figures 3-29 and 3-30 indicate that the Flathead River 

 (bracketed by stations 25 and 27) contributes significantly 

 to the nutrient load of the lower Clark Fork despite its 

 inherently low nutrient concentrations. The plots also show 

 that Noxon Rapids (bracketed by stations 28 and 29) and 

 Cabinet Gorge (bracketed by stations 29 and 30) reservoirs 

 act as sinks for phosphorus and reduce the Clark Fork load by 

 approximately the amount contributed by the Flathead. The 

 reservoirs apparently do not influence Clark Fork nitrogen 

 loads. 



Aquatic Macrophyte Problems 



Dense growths of rooted aquatic plants (macrophytes) can 

 affect lakes and streams in the same manner as excessive 

 algae growths. Aquatic macrophytes are usually found in 

 shallow zones and they derive nutrients from the bottom 

 sediments. 



The Pend Oreille River in the state of Washington below 

 the outlet of Lake Pend Oreille is plagued by extensive 

 growths of Eurasian water milfoil ( myriophyllum spicatum ) . 

 Growths have become so extensive that recreation, navigation, 

 water supplies, and water quality are affected (WATER 1987) . 

 The Eurasian milfoil problem is affecting Washington water 

 but it is a potential threat to Lake Pend Oreille and the 

 lower Clark Fork Basin of Montana. The plant is easily 

 transported to new locations by boaters, fishermen, or other 

 recreationists . 



Additional Monitoring Efforts 



Recent monitoring programs have improved our knowledge 

 of nutrients and algae in the basin. However, our knowledge 

 of these issues is insufficient for regulatory decisions. 

 Monitoring efforts must be sustained to identify long-term 

 trends, and fundamental questions must be answered about the 



3-91 



