The Duck Lake false spawn has got to be about the most fun there is in freshwater. Super difficult to have the perfect conditions, when it all comes together, and you're presenting your fly to schools of 10, 20, or 30 fish, it's unbelievable! Plus, the view of Glacier National Park from the eastside is maybe the most gorgeous backdrop in all of Montana.
Duck Lake, like most of the Blackfoot Reservation Lakes, are pothole lakes. They stock them with tons of 7 inch trout, there's a ton of food, and so they grow real big. Anyways, when there is no moving water, (but they've got needs ya know), they "false" spawn in the shallows. What it looks like is a big fat hen being followed by males. Sometimes you'll see 8, 9, and 10 pound fems being chased by as many as 30 males. Some will eat, some have no interest.
The problem is a wicked weather system over there. Yesterday alone, there were 20 mile an hour winds one minute, then dead calm the next; and that's an ideal day, usually the water is whitecapping all day this time of year. Obviously, to sight fish them, you need some sun, and only a ripple on the water. Otherwise, it's blind casting, and that's just dumb.
BTW, normally I wouldn't spill all this info on the net. But it's not like anyone really ever fishes this lake. Middle of nowhere, a sketchy reservation full of grizzlies, and terrible weather. No one would want to fish here.