The stonefly nymph trails off the Bobber Hopper hook.
August fishing means hopper time to many. But it's also a good time to take fish hunkered down in deep fast water. On the Green River below Flaming Gorge in Utah you'll even often see guides coaxing their clients into fishing large heavy nymphs below an inflated balloon. You can't cast that rig. They lob if off the back of the boat and then troll it with the guide positioning the fly (and the balloon) with the oars.
That's a bit extreme even for me. But with a fat foam hopper you can do much the same. With a slightly smaller rig you can actually cast.