We took our vacation up there in 2003, stayed in the little town of Canmore, east of Banff. An absolutely beautiful area, the Canadian Rockies are breathtaking. We rented a house there in a neighorbood. It overlooked Canmore and the surrounding mountians; the Three sisters sticks in my mind. We fished the Bow almost every day for a week. As was said earlier it is a glacial runoff river from Banff to Canmore, then it becomes more of a wide flat river. Still a big river at this point and not a lot of wadeable water. The current is strong, the bottom loose scree, it washes out from under your feet while you are standing there. The upper river is a brown trout fishery, and can be tough. I would have thought it would be a cutthroat stream, but evidently the mining in the early to mid 20th century decimated the cuts, it is all browns. We caught fish around the bridge in Canmore and the shrewd man would have himself positioned on the south side of the river above the bridge in Canmore an hour before dark ............. and sit on it. The last 30 minutes before dark (10:00 pm or so, gets dark around 10:45 - 11:00 pm) they would start rising and you could catch a few nice fish. If you weren't in that spot you were watching someone else catch the fish. They were 16-20" browns on dries. We didn't fish up in Banff National Park, wish we had. Our guide didn't have much good to say about it, but I still wish we had tried it. It is a beautiful aquamarine blue from the glacial runoff.
The lower Bow (1.5 -2 hours from Canmore) is below the dam in Calgary, it is a trophy rainbow fishery and you will catch 16+" fish with broad shoulders down there. Big River, they fish a nasty rig up there, and it is not fun to fish (indicator rig with 2 nymphs ~12' below a big indicator) but the catching was pretty fun because the fish are thick and strong. Another way to fish that lower section is to pound the banks with a large double bugger rig on a sinking line, of cours that was 2003 they may be doing thing differently lately, and we were there in July. We landed lots of nice fish in this section and would call it a pretty safe bet for a good day. Lost a realy trophy there as well swinging the buggers in a strong tailout or a riffle, the fish made two smoking runs across the river and got off 10' from me (heard that before, haven't you!).
There are other rivers in the area as well, the Oldman and another river a little further north in Alberta (Red Dear I think; known for big browns caught by site casting!) If I ever get back that way I will fish it at least one day!
We fished with a guide named Jeff Perodeau, a good guy 866 678-2486. We fished with him the second from 8 am to 10pm (no sh__!) I would be leary of the upper bow unless he says it is fishing really good, all I caught up there were whitefish!..... though my brother in law did stick and lose a huge brown. The scenery up there is breathtaking........... better than Yellowstone! But not the fishing..........
Any specific questions let me know, I will do my best to answer.