A lot of snow in the mountains this past winter creates a lot of water when it melts and "runs-off" in the late spring and summer months and thus often creates a lot of velocity as it melts and rips down the mountains finding its way to rivers and creeks below. Eventually the "flow" drops to the point when float boats can enter the water and fly fishermen can begin to fish from the boat for their beloved trout. Shortly thereafter, the height of the water drops and flow slows to the point where wade-fishermen can enter the rivers and creeks and fish from within the water.
The "run-off" report for 2011 based off of the 2010-2011 snowfall levels has read that fishing will be late this year. So naturally, the fly-fishing industry stands to take a hit as many vacationing anglers looking to book a blue water experience may be put off from doing so this summer.
Now, with the main river which feeds many of these other rivers and creeks, The Yellowstone, being poisoned by oil, the future is even more bleak for many of those outfitters and the like who make their living off of the various services they provide around the fly fishing tourism http://www.rocketnews.com/2011/07/high-water-hurting-montana-fly-fishing-industry-ap/industry.