Flathead Lake Lake Trout fishing in May is not for the faint of heart! On the largest, natural freshwater lake west of the Mississippi, weather changes occur rapidly, and along with making it hard to stay warm enough, or cool enough, it makes the fish turn on and off like light switches.
I have been hearing from many anglers that say they are struggling to even catch a lake trout, and truth be told, I have had a couple of those days myself! When 8 boats turn in 14 fish on a Mack Days Saturday...that's a major indicator that we all need to re think what we are doing. There are a few things you can do to help increase your chances of success.
Remember, unlike other lakes in the west that have Lake Trout, Flathead Lake does NOT have Kokanee Salmon, a major food source for Lakers. You must fish this lake different from all the rest, especially when trolling, as lakers feed on the bottom, not on the surface here.
Also, Flathead Lakes lake trout hate a crashing barometer. Small changes they tolerate OK, but big swings turn them off, right now. Stay on the fish, downsize and slow down your offerings. When and if the pressure starts to swing back up, like when the sky clears, then you are there ready for them.
Undoubtedly, when fish are neutral or negative...small offerings, like flies, small spoons, small tubes or hoochies will be your friend. A small dodger or flasher, even using a large spoon with the hook removed as a flasher is the right way to go. Watch your scent; don't give an already disinterested fish any more opportunity to ignore you.
Make your set back from the attractor to the lure a little longer, adding 6-10" can make that lure slow down enough to allow the fish to react without much effort. If you are using Yakima Bait Company Flatfish lures, consider downsizing to a T4 or U20 size. And slow it down. 1 mph is about right. If using hoochies or flies with Gold Star/Silver Horde dodgers and flashers go 0/0 or even 000.
Put it in their face. Know how far below the downrigger ball your baits swim, and adjust your depth accordingly. They aren't going to chase it when in these moods. A 50 KHz transducer gives you the wide angle you need to see your baits and downrigger balls on your sonar, and when tuned right you can track the ball as it drops, then watch that bait settle into its path. Know where that bait is.
Montanas Flathead Lake is muddy in May. The wind is coming from a different direction almost daily, spreading that mud line East-West some day's and North-South others. The schools of bait fish, Northern Pike Minnow (squaw fish) and Whitefish are on the move daily, and the Lake Trout (Mackinaw) are too. Find the clearer water, slow things down, use more muted colors and up your odds considerably.