conjunction with the MFWP observation of fishery impairment suggest that Lost Creek is 

 impaired as a cold water fishery. Abundant sediment, eroding banks, fish barriers and 

 sub-optimal spawning habitat all contribute to this determination. Whether aquatic life 

 support is impaired depends on several factors. As mentioned above, sampling of diurnal 

 dissolved oxygen levels is needed to determine if low DO conditions persist in Lost 

 Creek as a result of nutrient enrichment and/or dewatering and lack of shade in lower 

 reaches. In the event that DO levels threaten aquatic life in the lower part of Lost Creek, 

 control of aquatic macrophytes could be incorporated into the TMDL taking into 

 consideration all the possible factors that influence macrophyte growth. 



What are the causes and sources for impairment? 



Since TMDLs are required to establish all causes and sources for impairment, 

 development of a TMDL for Lost Creek should focus on linking sources, or actions, or 

 mstream conditions to water quality impairments. This often represents the most 

 difficult and resource consuming component of the TMDL process, particularly for 

 systems impaired by nonpoint sources of pollutants and/or habitat alterations. In the 

 case of nutrients, further study involving continuous temperature loggers and 24 hour DO 

 surveys during critical midsummer conditions should determine whether or not aquatic 

 plants in Lost Creek are responsible for diel fluctuations in dissolved oxygen which may 

 impair aquatic life support. Once determined, the linkage between nutrient levels and 

 their cause and sources can proceed. Quantifying the nutrient load contributed by land 

 application of wastewater seems the higher priority than estimating the nutrient 

 contribution from grazing practices, particularly since significant changes such as offsite 

 watering, corral relocation are already underway to reduce grazing impacts. Conversely, 

 impairment of habitat does not require further study and has obvious sources (eroding 

 banks, lack of woody vegetation, etc.) and causes (cattle grazing, hydrologic 

 modification, etc.). These components are therefore readily addressed through a phased 

 management plan (explained below). Developing nutrient targets to control aquatic 

 plants in Lost Creek would require additional modeling and sampling in the basin, 

 particularly to gauge the influence of land application of wastewater and cattle grazing. 

 Overall, restoring instream habitat and riparian habitat and addressing causes of their 

 impairment are most important to a Lost Creek TMDL, while nutrients from Lost Creek 

 are most relevant as a source to the Clark Fork River mainstem. 



Although a strong linkage between water quality targets (or thresholds for 

 maintaining use support) and pollutant sources or habitat degradation is a prerequisite for 

 acceptable TMDLs, a phased approach which relies on adaptive management may be 

 accepted by the EPA if reasonable effort is ongoing to establish these linkages and load 

 allocations (USEPA, 1999a,b). Therefore, without sufficient site specific information to 

 develop targets in advance of action, TMDL development can proceed with flexible 

 targets that may change over time. 



What are reasonable targets for water quality? 



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