Barrier & Entrainment Study

Executive Summary

Friends of the Teton River conducted an assessment of potential barriers to fish movement and potential entrainment hazard on 14 tributary streams to the upper Teton River.  Most streams were walked or floated in their entirety, from the foot of the Teton or Big Hole Mountains to the Teton River, during the search for barriers.  A total of 59 potential barriers and entrainment hazards were inventoried.  Each barrier was assigned to a relative degree-of-barrier class via a qualitative assessment of barrier height, construction, and flow conditions.  24 barriers were assigned to the low or non-barrier categories, 7 barriers were assigned to the low-moderate or moderate categories, and 13 barriers were assigned to the high barrier category.  Three barriers were assigned to a low-high category due to very different conditions observed over a range of flow conditions.  Entrainment potential, or the possibility for fish movement into an irrigation canal, ditch, or pipeline was also assessed.  Entrainment potential assignments were based on the volume of diverted flow relative to the natural stream flow, the construction of the diversion, and the condition or “naturalness” of the diversion canal or ditch.  Entrainment potential was either low or not applicable (for example at culverts) at 27 sites, low-moderate or moderate at 17 sites, moderate or moderate-high at 15 sites, and high at 6 sites.  Four of the larger Teton River tributary streams possess only a single barrier to fish movement deemed to be a high priority for alteration based on the degree of barrier, entrainment potential, and location with respect to the known distribution of native versus non-native fish populations.  Two streams had two separate barriers ranked as priorities for alteration, one stream had three, and one stream had four priority barriers.  Alteration or reconstruction of these barriers could potentially reconnect isolated fish populations and allow fish to safely use high-quality spawning habitat located in the valley segments of these streams.  It should be recognized, however, that few isolated populations of native YCT remain in the mountain portions of Teton Basin streams.  Removal of barriers on these streams could allow non-native trout, particularly EBT, to pioneer these pristine waters, possibly displacing YCT.        

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Maps from the study