Lucky Peak mud

Answer:  What happened with the flash floods in the South Fork and Middle Fork Boise River drainages was a unique event that most of us have never experienced before – at least in this river system and our lifetime.  Intense rain on recently burned slopes released mud and debris into what was a relatively stable river system. With the floods in the South Fork and Middle Fork Boise Rivers, we expect a decline in the overall trout population over the next few years as the forces of nature reshape the riverbed substrate.  Changing flows will sort materials and create new spawning and juvenile fish rearing areas.  Once the river is again relatively stable, we expect the wild trout populations to rebound higher than before the floods due to increase diversity of habitats, the introduction of more woody material (fish and aquatic insect habitat) and an increase in nutrients (carbon) the aquatic ecosystem needs to thrive. Last summer when the floods happened, the water column in Lucky Peak and Arrowrock reservoirs were stratified by water temperature.  Cold water was on the bottom of the reservoirs with warmer water on top.  What we suspected was happening is, the mud-laden run-off was flowing along the bottom of the reservoir in the cold water layer and being discharged into the Boise River through Lucky Peak's deep-water collection system.  We anticipated that once the different temperature water mixed/turned over in the fall, the mud would settle and the Boise River through town and Lucky Peak Reservoir would again appear clean.  As we both know, that has not happened. What impact will the sediment in Lucky Peak Reservoir have on stocked rainbow trout and kokanee?  Our best guess is, it could actually improve growth rates on rainbow and kokanee and make the fishing better.  Fish growth in Lucky Peak is dependent on both phyto and zooplankton.  The Boise River system, when compared to many river systems around the State of Idaho, is lacking base nutrients.  This flood event may have increased the nutrient level in the reservoir, which in-turn, will improve plankton biomass (food).  We could and should see benefits, especially to the kokanee growth rates in Lucky Peak, as early as 2015.