Ontario fly fishing is a great way to pursue Brook Trout in our big rivers of Northwest Ontario. Much of this relates to my own experience on the Dusey River but should crossover to the Albany, Opichuan and others.
Nymphing: In my opinion nymphing is one of the most effective methods you can use to catch Brook Trout on the Fly. I recommend using a strike indicator and a 10 or 11 ft. leader with 2x tippet. Fluorocarbon works well. A bb shot or two is all you will need to weight your leader in many areas, including fast runs and tail out areas while you will need more to probe the deep corner holes. Versi leaders and sink tips with a sink rate of 5-6 inches per second can be helpful. I recommend a rod of 6,7 or 8 weight, 9 or 10 ft. in length. I prefer large arbor reels.
Flies: Here is the short list of nymphs you will want in your box- Olive hares ear- size 10-12. gray hares ear-size 10-12. prince nymph-size 8,10,12. Caddis larvae ( green rock worm) size 6,8,10. Stone flies- Black- size 4,6,8. Brown-size 6-8. Golden- 6-8. There are many variations of the stone fly nymph, some with attracter colors or legs tied in, some are weighted, I suggest trying several, you might find a variation that outperforms others. Brown and Gold have done well. Superior xleg- size 6,8,10. Brown, Black.
Note: Wooly Buggers fish well with this method too. Try Brown or olive in size 6 and 8.
Streamers: Fishing streamers can be very rewarding, especially when water temperatures approach 50 degrees Fahrenheit. Brook Trout are often hooked on some pretty big flies on our waters. A couple of season's back one of our guests caught and released a 27 inch Spec on a size 4 olive leech imitation. I fished with a fellow a few years back on the Dusey who was throwing a white and red streamer he had tied that must have been 4 inches long and he hooked a lot of nice fish with this fly, with aggressive, even explosive takes. These trout are prone to hitting big flies and lures with combinations of red, yellow, white, olive, chartreuse, pink, black, orange, gold, even blue and silver. Fishing the down and across method works well. I like 2x tippet and in really fast heavy water even 1x. Many areas can be fished with full floating line but you will want to have a versi leader (sinking) or even a sink tip or full sinking line for the deeper or heavier water you will encounter.
Flies: Leech imitations-size 4,6,8 colors-olive, white, black. Mickey Finn-size 4,6,8. Muddler minnow and Marabou Muddlers-size 4,6,8. Egg sucking leech- size 6,8-purple,black. Crystal buggers-size 4,6,8. Olive, Purple. Multi Buggers- size-4,6. Wooly Buggers- size 6,8. Brown, black, Olive. There are obviously many more streamers that will work for you. Basically, if it is Red and yellow, Red and White, Chartreuse and white or olive and white, try it.
Dry Fly fishing: May fly and Caddis are present here and once the hatches start fishing dries can be exciting. Also, skating or dead drifting small mouse imitations in the evening can be a good bet at times with violent strikes when the specs hit. This is often best in the low light periods(early morning, late evening). Lighter tippets may be helpful but I like to start a little heavier and down size if needed. These Brook Trout are really strong and can strike explosively, and the water is heavy with strong currents, so be prepared for an occasional break off if you are fishing light tippets. I recommend 9-10 ft. leaders with 2x or 3x tippets.
Flies: Elk hair caddis, Royal Wolf, Adams, Black Gnat, Blue winged olive, various Hex patterns and Deer hair mouse patterns. There are obviously other Flies that will perform well but this is a start.
General info: You will need stocking foot chest waders with either felt soled or studded soles on your boots. Rubber soles with out studs are not safe here. I also recommend a wading staff for extra stability. These rivers are very rocky and swift, with rock on rock bottom in many cases and wading can be challenging. Play it safe. These rivers are big with lots of current and open areas for wind to drop into so I prefer 7 and 8 weight rods, 9 - 10 ft. Switch rods will work well here too. We have had guests bring center pin rigs with longer rods ( over 12 ft.) and this has worked well. You will need a net to handle the Trout and release them unharmed. They are very slippery and never quit fighting you, even when landed. This will allow you to snap a quick photo and get the trout back in the water right away. Mosquitoes and Black flies can be real tough by early June so bring your DEET. We have found the Simms Bug Shirt to work well and fingerless sun gloves too, ( to keep from getting the backs of your hands bit up) and recommend both. Amber or copper polarized glasses are helpful and should be in your gear bag. Soak in the beauty of some of the most pristine wilderness river settings you will ever find and enjoy.