Air temps this week are predicted to be in the 60's every day, with nights mid 30's to mid 40's- this will push water temps up for better fishing as the week progresses. If fishing below the Still River, the water is higher, so think nymphs & streamers, and fish closer to the banks, anywhere there are current breaks. Look for wider pools & also inside bends. Higher flows scare many fishermen away, but the fish are still there and catchable if you approach them correctly. They simply move closer to the banks, out of the heavier current. You can upsize your nymphs & streamers, no need for light tippets, and make sure to fish your flies slowly, down near the bottom.
I did well after work on Opening Day, catching a bunch of trout on nymphs, including a nice broodstock brown. Fishing reports have varied greatly, depending upon the day and who you talked to, with some anglers doing quite well and others struggling- cold than normal water temps for Opening Day weekend made for sluggish trout last weekend. As flows drop & temps warm this week, look for afternoon water temps to push well into the 40's. Up in Riverton, temps will stay colder due to cold water release from the bottom of the dam (still mid/upper 30's up there in the mornings, but warming by the afternoon on sunny days). So from the Still River downstream, especially on mild/sunny days, the water will be noticeably warmer, which often translates into more active trout. 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, especially 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). Big, flat, wide pools like Church, Greenwoods, Whitemore, Campground & Beaver Pools are your best bets if you want to fish dries. The Winter Caddis (AM) are waning but you may still see some, in the afternoons you should see Oives (#16 Baetis Vagans), Midges (#20-28) & Early Stones (#12-18). 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 up near 50 degrees (probably late April if you are downstream of the Still River).