Fishing has been quite good throughout the Black Hills. Definitely a bit of high water, but flows have been dropping on most streams.
Rapid Creek is the highest, but flows below Pactola lake have dropped enough to be fishable. 80-90 CFS below the lake is about the sweet spot, so we have a little ways to go. There are fish to be had below the dam if you're willing to fish a little bigger and a little heavier than you normally would. Fish a big worm or scud for your lead pattern, and fish a small BWO or Midge as a dropper. You can do well on goofy stuff like mop flies and Pat's Rubber Legs sometimes as well, so don't be afraid to mix it up with the higher flows. With the current flows being higher than normal, search out the softer inside edges and obvious current breaks to find the most fish.
Rapid Creek in town is high but fishable, and has been fishing well. Fish with larger flies and focus on anywhere where the water has some depth and is moving around walking pace - it doesn't have to be deep necessarily, but the ideal water will be considerably slower than the middle of the river. Squirmy Wormies, Mop Flies, and large jig patterns are good bets. If you run across some pickier fish, try a smaller jig dropper or a midge of some variety. There's a surprising amount of fish that hang out really close to the bank when the water is high, so don't be afraid to hang back and fish the first 3-5' from the bank if it looks fishy. The fish are super healthy after a couple years of higher than average flows!
Spring Creek has been fishing great and is at a very nice flow, but it has probably been the busiest fishery in the Black Hills. Since Rapid Creek is quite high, Spring Creek has been taking the brunt of the pressure since it's only 20 minutes from town. That being said, it's still fishing very well. There is a really good Blue Winged Olive hatch in the morning, and the fish are definitely eating them. They can be rather picky some days, but if you mix up your flies enough you'll figure out what they like. The naturals are pretty big, so fish flies in the 14-18 range. Sparkle Duns, Brook's Sprouts, F Flies, Students, and various other BWO patterns can all work. If there's no fish on the surface, the nymph fishing has been good on smaller flies. Split Back BWOs, Pheasant Tails, Flying Zebras, and various other small droppers in the 16-18 range will pick up plenty of fish. Fish them behind a heavy tungsten jig in 12-14 to help get them down quickly. The trailhead has been fishing well but has seen the most pressure - Spring Creek is fishing well throughout it's length, so it's worth poking around some other areas as well.
Spearfish has dropped into very nice shape and fishing will pick up there as a result. Nymph fishing has been the best bet over the past few weeks, but the terrestrial fishing should really pick up with the warmer weather. There have been good numbers of caddis around in the evenings, particularly on the lower stretches. Bloom's Parachute Caddis and Elk Hair Caddis are good bets in a size 14 or 16. The nymph fishing has been good throughout the day, with smaller dropper patterns picking up the most fish. Flying Zebras, Skinny Jigs, small Jig Pheasant Tails, Assassins, and Perdigons are good flies. The flows are great, and there are fish spread out in all types of water right now. The upper canyon has been fishing well with dry/droppers as well - try a Klinkhamer or Hippie Stomper for your dry with the same droppers as you'd use on a nymph rig.
Box Elder is also at a near perfect flow now. The fishing from Steamboat Rock upstream to Boxelder Forks campground has been great. Dry droppers will be the ticket from Nemo upstream, but further downstream you may need to fish slightly deeper with an indicator. Lots of different flies will work well - Duracells, Assassins, Peacock Jigs, Hare's Ears, French Dips, Gum Droppers, and various other tungsten nymphs in size 14-18 will work well. Try a Micro Chubby Chernobyl or a Hippie Stomper for the dry in the dry/dropper rig.
Summer hatches are picking up- good reports of Caddis activity on Spearfish. Still seeing a few blue winged olive mayflies. Some stoneflies around yet too. Should be in good shape to fish dry dropper rigs in most places. Attractor dries like the fabled Hippie Stomper are a great option for the dry in the dry dropper rig.