At the time of this writing, only the Lost Creek data collected from 1989-1991 

 were available to supplement water quality data collected in this study. Montana DEQ 

 will only accept biological, not chemical, data over five years old as sufficient credible 

 data. Guidelines for sufficient credible data and beneficial use support determinations 

 are available from the Montana DEQ (www.deq.state.mt.us). However, water quality 

 data gathered in this investigation meet minimum requirements for an acceptable level of 

 information to make such determinations. Using impairment guidance, these 1999 Lost 

 Creek data indicate a moderate impairment by nutrients at most sampled stations on Lost 

 Creek. In addition, the assessments of stream and riparian health should also meet the 

 minimum requirements to determine that the majority of stream reaches (>70%) are 

 severely impaired by habitat alterations. However, additional information on the 

 impairment of aquatic life support needs to be gathered to supplement these 

 determinations in order to achieve a clear picture of the impairment. In this case, the 

 DEQ should work with the MFWP to develop fishery guidelines, and the level of 

 information required (i.e. # of assemblages, biotic indexes required). 



Are beneficial uses impaired? 



Currently, the beneficial uses of coldwater trout fishery, contact recreation, and 

 aquatic life support are listed as moderately impaired over the lower 17 stream miles. At 

 the present time the rationale for this determination is unclear, and the data supporting it 

 is likely outdated. MT DEQ has re-issued the 303(d) list in April 2000 with significant 

 changes in the priority level for TMDL development for Lost Creek. The 1998 303(d) 

 list established a low priority rating for TMDL development for the lower 17 miles of 

 Lost Creek. Based on a new scoring and evaluation method, the DEQ has raised Lost 

 Creeks priority to the second highest priority stream in the Upper Clark Fork River, with 

 a score of 52 points compared to 53 points for The Little Blackfoot River. However, the 

 question remains whether Lost Creek is impaired by nutrients, given that there was very 

 little observable algae growth in the creek, due mainly to insufficient rocky substrate for 

 algae to attach Abundant aquatic macrophytes were observed in the fine substrate found 

 in the lower reaches. However, it should be determined if their growth constitutes 

 nuisance levels by evaluating diel fluctuations in dissolved oxygen. Without further 

 investigation, gauging impairment caused by elevated nutrients is problematic since the 

 state of Montana has not formulated numeric criteria for nutrients. However, use 

 impairment criteria assume that waters are moderately impaired for nutrients if levels 

 exceed reference conditions by 200% and severely impaired above 400% of reference 

 (MTDEQ, 1998). Although a reference stream was not identified for Lost Creek, several 

 stations (5-9) exceeded background values (represented by upstream Station 1) for nitrate 

 by 200%, and Dutchman Creek nitrate levels were in excess of 400% of Station 1 levels. 

 Although it is unclear whether high nitrate levels impair beneficial uses in Lost Creek 

 itself, TMDL development for nutrients should consider Lost Creek's contribution of 

 total and soluble nitrogen to the Clark Fork River. 



Habitat assessments indicate that 70% of the stream length surveyed is not 

 functioning properly. The stream and riparian condition indicated by these surveys, in 



