Every fishable mayfly 'hatch" in the Spring branch is either cream or celery colored and size 18-24, they are baetis and hatch out of weedbeds (if you wanna get technical about it) and the spinner fall happens over land.
The "pale evening dun, and the PMD" that you hear about all the time (via Weavers report and from JR) doesn't even exist at BS.
The Caddis's are coffee bean brown with slate wings, and #20 (they are divers so the "hatch" really isn't a hatch, it is egg laying. And they die mid-stream or in the surface film after laying their eggs. The crawl to the bank to "hatch".
Midges are creamy gray and smaller than any hook made...but a #26-32 works.
There's a lime green/red legged hopper hatch in June (#10)
Those are the only dependable/fishable "hatches" at BS as far as I know.....except for the "Gut hatch".