I grew up in Red Deer. I watched the RDR change over my lifetime. I must admit, however, that I did not fish it when it was in its brown trout prime. As a teenager in the late 80s, it was possible to catch walleye, pike, goldeye, whitefish, and rainbow trout (yes, rainbow trout) in the city section. So, as long as I can remember, unless you were very specific (like bottom bouncing a sz16 fly tipped with a maggot for whitefish or chucking a big red devil for pike), at least to me, it has always been a piscatorial roulette. Oh, the things a kid could catch with a small panther martin spinner!
I had not fished the RDR since 1992. I took up fly fishing about 12 years ago. I immediately started fishing the RDR, mostly for whitefish and goldeye, as a homage to my childhood. I remember the first brown trout that I caught. I had a WTF moment. I was expecting to set the hook on a 12" whitefish, but was actually a 24" brown trout. Since then, I have caught a steady 1 or 2 per year in an average of 4 or 5 outings per year. They do not live in your typical brown trout lies---those places are occupied by walleye. They live with the whitefish---kind of like a herd of house cats living with a lion.
There is no doubt the brown trout population is in a tenuous balance with all the other species. The brown trout fry have a gulag/gauntlet to run to outsize the walleye, but if they can make it to 12", really, they only have the pike to worry about, and a big brown trout predator has a veritable cornucopia of food sources.
They are very wiley; they would have to be to survive in the chaos of the RDR. But if you can catch one, they really are an archetype of the species---very beautiful.