Dearborn River Report
June 22, 2010
It's a river that goes under the radar by many throughout the state, but it's a river that should be near the top of any trout angler's bucket list for Montana streams. The Dearborn River is viewed by many as a low water, small trout stream whose sole purpose is to feed the Missouri with rich, cool mountain water. Wrong.
I began floating the Dearborn last year and was pretty skeptical about it to be quite honest. I've heard rumors/stories of really big brown trout that call this water home, but had only seen the water at highway 200 and 287 bridges, making me feel that the rumors I had heard were merely lies. My first floating experience was a good one as far as taking in the scenery, but the fishing was poor to say the least.
We boated close to a dozen fish, none over 15" and tried every technique known to the sport of fly fishing (some were probably even made up). At the time I was really upset and didn't understand why we weren't able to boat or even move a fish pushing the 20" mark. The water looks absolutely perfect for holding big fish, that kind of riffle, pool, pocket water that makes you feel like you're floating Box Canyon on the Blackfoot.
As opening weekend came around this year, I was ready to float and was hell bent on boating a fish over 20" mark. We had a different game plan this year, which consisted of throwing ridiculously huge streamers on sinking lines with complete confidence that a big fish would eat. This strategy paid off in a big way, ultimately leading to seven fish that pushed to and beyond the 20' mark with in two floats this year (and moved more fish than I thought were in the river).
This started to get me thinking. Why aren't these fish eating stoneflies, caddis, pmds, and terrestrials on a regular basis, and why aren't there overall more fish in this river system?
Then my analytical mind began to take over. The river is only floatable for a short period of time beginning the third Saturday in May (opening day) until the flows get too low (usually by the middle of June). Its prime floating level is over 350cfs, with most comfortable levels around 500cfs. Doing a little research, I was surprised to find that the river drops down to and below 100cfs by the middle of July and throughout the rest of the summer and into autumn.
Last year the river dropped to 41cfs on September 30, which is a mere trickle. Its flows throughout the winter are also off the charts do to ice, which tells me that the stream is at extremely low levels. Based off the flow charts and the size differences in fish caught between years (and techniques used), I feel that the Dearborn is a major migratory fish river. This means that larger fish do not reside in it year round, with exception to some fish. It is documented that the Dearborn is a major site for Missouri River rainbows to spawn and that is why it is closed from December - May. Knowing this helps with the assumption that larger brown trout will follow the push of rainbows up the river in early spring to feed on their eggs (same goes for the whitefish spawn in late fall/early winter when flows allow it).
After the bows do their thing and vacate the river, I believe that the majority of the larger fish, bows and browns alike, will migrate back to the Missouri. As always, there is an exception to a rule and in this case, some of the larger fish will stay in the river for longer than intended. These are called hold-over fish, and they will sometimes stay in the river for a week longer than intended or will call that river their new home. This is why I consider this river one of hit or miss.
Some years, much like this year, flows will stay at a level that will allow larger fish to remain in the river longer than intended. The larger, migratory fish will exhibit predatory instincts when they are introduced into a system filled with smaller, less aggressive fish in it, therefore, it requires techniques that trigger and initiate a predatory response. Streamer techniques are obviously one of the most effective ways to initiate a predatory response, but other techniques including nymphing with big, leggy stonefly nymphs or fishing large salmonfly/golden/attractor patterns can initiate an aggressive response too.
Overall, the Dearborn does have fish that reach over the 20' mark, but don't expect to knock um dead every year. This river is a major hit or miss river in Montana and will remain one of my favorites for that reason.