November 2013

Mainstem Snake River

In the minds of so many fly-fishers the Snake River from the Henry’s Fork confluence downstream to American Falls Reservoir takes a back seat to the South Fork reach (Palisades Dam to the Henry’s Fork confluence and to the Henry’s Fork. Perhaps it is because the best fishing on the main stem is very seasonal and also because access to the river is more limited because of the vast expanse of private land through which it flows. Best fishing is seasonal mainly because when the irrigation season begins water to satisfy demands makes successful fly-fishing more difficult to come by.  High and fluctuating flows during that season make wading more dangerous than in many area waters and can also influence boating.  Nevertheless success can be found  at certain locations.  BWOs and PMDs can be seen emerging in season, and when flows begin to drop and stabilize around Labor Day a legendary snowflake dun emergence begins on the river. It is heaviest from just below Blackfoot down to the reservoir.  In August when waters are almost always high a hexagenia emergence takes place from certain locations along the river.  Silt is required as nymph habitat for this giant mayfly.  One location where this is present in quantity is the river bed going through Idaho Falls.  Specifically this habitat is above the power plant diversion forming the still water just above the Broadway Street Bridge up to the John’s Hole Bridge.  Another good habitat location is in Gem Lake a few miles below town.  Hexes emerge in the evening and during nighttime.  Some of them find their way to building fronts in town, and it is comical when a puzzled fly-fisher comes during morning into the shop holding one and wondering “what the h— is this? Do PMDs get this big?”  So yes, there are mayfly seasons on the main stem, and there also are numerous caddisfly, yellow sallies, and midges emerging almost year round.  Best time for the BWOs is early in the season before irrigation water takes over, then later after it is mostly gone.  During these times BWOs can be seen just about anywhere on the river. Same with midges and caddisflies.  So when low waters come around and overcast or storms prevail a BWO experience from walk-in wading at  select locations can rival those on the South Fork and Henry’s Fork

One fact that many fly-fisher find tough to accept is that there are more truly large fish in the main stem Snake River than in the South Fork reach or the entire Henry’s Fork.  And the best way to encounter these is through presenting streamer patterns (sink tip lines, short stout leaders, and seven to eight weight systems). This is true even during high water times, but then such as fast sink tip lines are necessities. Even lead core lines to get down in calmer sections can work. Yes  it was caught through using bait, but the state record rainbow trout came from the river below Tilden Bridge, and bait fisherman take double figure poundage browns and rainbows year round. In years gone by, cutthroat trout this size were common in the river.  For the fly-fisher the best time to encounter the large trout this part of the river offers is from the end of irrigation season through winter and on until irrigation season begins.  Much of the river can be safely waded, and fish are concentrated relative to during the high water season.  At these times, as always when fly-fishing, presentation trumps fly pattern selection.  Have bright and somber patterns in the fly box.  Expect best fishing during low light conditions, and when bright sunlight prevails, seek  parts of the river out of direct light.   Locations during low water are aplenty, and the best way to make a selection is to come to the shop and discuss “where to fish” with us.