Had some good fishing here last week on my days off, with my girlfriend Mandy putting on a virtual clinic Wednesday 4/15, racking up trout after trout on nymphs in front of a crowd, including a big brown landed and a low 20" range 'Bow hooked & lost at the net, it was well over 4 pounds, grrr. Water temps have been ranging from upper 30's to upper 40's. Riverton has been upper 30's in AM, and on sunny days getting into the low 40's. Down in the permanent TMA, morning temps have been low 40's, reaching as high as upper 40's/low 50's on a sunny afternoon. Those who have found pods of freshly stocked trout recently have racked up the biggest catches, but some bigger holdovers are mixing in here & there. Fish a spot, but if it's not producing, move on, don't linger. Lately the more water I cover lately, the better I do. I might come up empty in 2-3 spots, and then bang fish in the 4th. Nymphs & deeply/slowly fished streamers are the most reliable fish catchers in the cooler waters of the early season, doubly so when flows are up. The dry fly guys have been back at it when flows have been normal, and catching some fish at moments (ideally look for days without much wind)- overall the dry fly fishing has been slow lately though. This will change in the next couple weeks as water warms and we start to get into the hatch cycle. The Winter Caddis (AM) are waning but you may still see some, in the afternoons you should see Oives (#16-18 Baetis Vagans), Midges (#20-28) & Early Black Stones (#12-16). With the Caddis & Stonefly dries, try both dead-drifting them and also lightly twitching them, Baetis & Midges should mostly be dead-drifted. Sometime in late April we should see the first Hendricksons, they will probably be a little late due to the brutally cold winter.
Subsurface, it's not too early to start fishing Hendrickson nymphs, they get active and end up in the drift a good month before the hatch begins, and Bruce Marino & Rich Strolis both tie us DEADLY nymps for this- ask and we will point you toward them. Hendrickson nymphs catch me a lot of BIG trout in April/May. A bigger #12-14 Pheasant Tail can also work well. Hendrickson Nymph patterns can also pull double-duty as early season stoneflies. #16 Olive nymphs imitating Baetis Vagans are also a good choice now, they are just starting up. Early Black & Early Brown Stoneflies (sz 12-16), Pheasant Tails (sz 12-18), olive/green caddis larva (sz 8-16), cased caddis larva (sz 8-16), midge larva/pupa (sz 16-20, especially in red), attractor nymphs (sz 12-18 in Red Headed Stepchild, Copper Johns, blue Lightning Bugs, Yellow Prince, Rainbow Warrior, and egg flies (sz 10-18) are still a good choice (rainbows & suckers are both spring spawners in March/April, contributing fish eggs to the drift), etc. Don't be afraid to fish some some gaudier/flashy/attractor-type nymphs, the trout sometimes show a preference for them, doubly true for recently stocked trout.
If you are fishing streamers, remember that a slower presentation (swinging and/or slow stripping & twitching) matches up with the slower trout metabolism due to cooler water temps- but as always, play with your presentation and let the trout tell you how they prefer it, they may still want a bit faster strip at moments. Try using a floating line and slowly bouncing/hopping a weighted Fishskull Skulpin Bunny on the bottom- use a 0x-2x tippet with this pattern & method, that fly is heavily front-weighted and rides hook point up. If you are using unweighted or lightly weighted streamers, use something to get them down- sinking line, sink-tip line, sinking leader, or split shot. Slow & deep is typically the name of the game until water temps get over 50 degrees and stay there (probably late April if you are downstream of the Still River).