Try a little research, nearly all the problems associated with the decline in anadromous fish in the Columbia/Snake River drainages are dam related problems. Just a fact.
Many of the things being discussed on this thread as parts of the problems are all associated with dams.
Lets look at a few:
Sea lions...yeah, they kill adult fish by the truckloads below Bonneville. Why? Because the fish stack up below the dam where they're easy pickings. Mink in a henhouse situation. Are sea lions the problem? Wouldn't be an issue if the dam wasnt there.
Predator fish species (walleye, smallmouth, pike minnows, etc.) all caused from impounded water behind dams. Water that doesn't flow, warms up making it conducive to warm water species. Add into that highly increased time for smolt to have to SWIM head first through miles of slack water, with huge numbers of predators, well...you can fill in the blanks.
The other problem with smolt survival is how long they have to stay in the rivers with dams present before they reach the salt. In a natural flowing system, during high water...they get flushed to the salt TAIL first and they get from the upper reaches of the tributaries in weeks. The less time they spend in fresh water, the less likely they are to get picked off by predators and they healthier they are when they reach salt. Think of the energy requirement of a smolt, that has to swim head first through miles and miles of slack water, compared to that same smolt getting essentially flushed into the salt in a few days.
Spawning habitat has been inventoried in the Selway, Snake, Salmon, etc. rivers and their tributaries. Lots of work has been done to make fish friendly culverts, etc and the Idaho F&G as well as USFS have studied the viability of the spawning habitat. Generally the spawning habitat is in very good shape, but, when you don't have adult fish getting to that habitat to spawn, does you no good.
Frankly, its amazing that anadromous fish have hung on as long as they have in the Columbia, nothing, and mean absolutely nothing has worked in their favor since the first dams were installed.
Anyone that questions if dam removal will work, is defying science, logic, and just plain g-damn common sense.
If you need further proof look to the Fraser river system, where there aren't dams just to the North of the Columbia. Not much drags me away from big-game hunting, but I spent a lot of time fishing the Fraser and its awesome tributaries in the fall. Made fishing in Idaho, which I did a metric chit ton of, look pathetic.
There is one major difference between the Fraser and Columbia...I'll give you 3 guesses what that major difference is between the 2 river systems.
Finally, as to the importance of moving smolt downstream fast...look at the winter of 1996/1997 as the perfect example. That year was a monster for snowfall, as well as good spring moisture as well. The dams on the Snake and Columbia were flushing water as fast as they could...
This was in mid November, hunting wayyyy lower than normal due to the heavy snows already hammering Idaho and Western Montana in 1996.
I remember fishing steelhead in the spring of 1997, it was tough because of the amount of water. Dworsak was flushing heavy, upper river between Clear Creek and Orifino were so high it was almost unfishable. South Fork was blown out.
But, fast forward to 1999...unbelievably good returns on both steelhead and salmon. Why? Because smolt moved to the salt in a hurry. High smolt survival, high returns 3 years later.
I'll never forget that year, I landed 106 kings fishing from the bank...and I didnt fish all that much to do it. The towns of Riggins, Kamiah, Orifino were all bustling. Motels booked solid, RV spaces didnt exist, camp grounds plugged, guide shop in Orifino was booked solid for the entire season. Waiting in line at restaurants in Kamiah? I remember buying ice at a local tackle/shop gas station in Riggins, the guy said go check to see if I have any first. He told me he had 3 ice deliveries that day, 500 bags at a time. The only tackle he had left was a few packages of hooks and a single roll of pencil lead. It was just crazy...huge economic boost to those communities.
If you build it, or in this case, remove them...they will come...and in droves:
Finally, I applaud Simpson for taking this step, something that should have happened a long, long time ago...