We went to St. Mary last weekend and had success!
Here's the report:
Friday afternoon (day 1), we arrived at Lakeside Gardens, and checked in. The water was very clear, compared to the algae ridden lake we came to years ago. Zero surface activity, and not many bugs flying around. Rigged up the type-2 clear sink with a dragonfly pattern that worked wonders during previous stays, and went searching.
Armed with a #6 deerhair diver, started our way around the perimeter of the lake on the boat. Anchoring 30-40' from the shoreline (roadside), casting just short of the weeds, we started hooking up right away! First fish was a good size, eyeballed at about 14-16 inches. Later fish were in the mid size, 10 inches or under. Lots of action along the edges. Didn't make it to St.Mary Lake Resort side that afternoon, as there was plenty of action where we were.
Dry patterns that worked (that I tried): deerhair poppers and divers, foam grasshoppers, caddis and sedges.
Wet patterns that worked: dragonfly nymphs, wooly buggers, leaches, attractor nymphs with rubber legs, rolled muddlers and other minnow patterns, and chironomids under an indicator.
In the evening, there were consistent risers along the shore, so I parked myself and tossed out a size 8 chronie 3' under the indicator near a rise for near instant hookups. As the rising action slowed, I would lengthen the distance between fly and indicator for continued success, adjusting up and down based on activity.
Once it got dark, we headed in.
Saturday (Day 2): It's a bit cooler in the morning. Was hoping for some trout, so I went deep with only bass to show for it. (forgot the faster sink lines at home). I tried a foam popper with lots of flash flanking the tail, that hooked many top water bass, keeping the morning interesting. Good action along the edges and many drop-offs. One of our guys tried the other side of the lake in the morning with great success with bass poppers and crank baits, among other lures he uses for huge black bass in Japan. (there's a gravel road/hiking trail on that end) So we decide to join him over there in the afternoon. The clearer water and overcast skies helped us see the drop offs and sunken logs and rocks, where bass could be hiding out. Casting into these areas gave us multiple hits, and big fish!
Closer to evening, I visited my friends staying over at St Mary Lake Resort, and took some of the kids out on the boat. Same story, with fish hiding along the weedbeds, under trees, sunken trees, docks... basically anywhere there is underwater structure for them to hide. Since while on the move I wasn't trolling super deep, we'd only catch along the shoreline. Straight across from the resort, there are weedy shallows that were home to several large bass, that the young kids were able to hook on bass lures. The rolled muddler lost all it's deerhair collar/wing by the end of the evening!
Sunday (day 3): Only time to fish in the morning, since we're catching the 3:30 ferry out. We get on the boats at 6am and head for the other side of the lake opposite the island. We briefly try casting into the drop-off near the 'island', with no result. We continue to the weedbeds and start to hook fish right away. Since the sky was not reflecting off the water at that time in the morning, it was really interesting to see the rocky drop offs on that side of the lake. Figuring there would be fish hiding against the underwater "walls", we anchored and hooked a few fish. Wanting to try other spots, we let the boat drift with the water, taking us counter clockwise around the lake. Not fearful of losing a fly or two now, I tried casting deeper into weedbeds, where the water would open up a bit after the initial row of weeds. The trick being, I would pick up my line before the leader was in the weeds again. REALLY big fish hiding in there! It's a shame the lil boy I had on my boat would keep casting into the trees or get stuck on a weed, so I'd have to take the boat right in there to retrieve the lure. So we'd keep moving on.
We finally got ourselves to the weedbed accross from St Mary Resort again, and was able hook into some nice big fish in the same area. Great hot action in that area. Closer to noon, we decided to head back to the dock, so I could get my stuff ready for our trip back. My friends were staying an extra day, so I hitched a ride with our friend leaving on Sunday as well.
I learned a bit more about the lake this time, because I was able to see deeper into the water, and study the kinds of hiding spots the fish were holding in. With that knowledge, we increased hookups by finding similar locations. Also, we noticed that our hook rate with poppers with rigid weed stoppers kept fish from staying on the hook or from hooking entirely.
After coming home, I receive the report a day later about the fishing after I left. Trolling with minnow lures brought in some really nice sized rainbows for some of the kids who stayed an extra day, with bass being caught near the docks and elsewhere while on boats as well.
All in all, I averaged 20-40 bass a day, depending on whether I would cast and retrieve or do some searching by trolling. Casting and retrieving was more successful by far, as long as you were casting into the right area. In total, maybe 6 trout (cutthroat and rainbow) caught on nymphs and muddlers. Half by trolling, half by casting.
There are more/bigger trout on the St.Mary Lake Resort side of the lake. When the hatches are on, that area is insane! Otherwise, the bass are everywhere in the lake.