They can be .... I've caught some bruisers from there, before (as in decades ago ). My suggestion would be to use minnows, fish at night under lights, either in Tanyard Branch or McKecknie Branch. Tie off to standing timber & put your minnows down at about 8-12ft deep. If you draw Shad, but get no bites within an hour ... move.
Now, you're probably not going to catch Crappie in the 2lb range (and if you do I want to know WHERE you did ) ... but, there is no size limit on Crappie at Herrington, just the 20/person/day creel limit.
And if you're limited to fishing for them during the day, those same two creeks would be where I'd go, but "I" would probably be casting jigs around the standing timber or private boat docks. That is, of course, if there's any timber still standing. Like I said ... it's been decades since I fished up in either of those creeks, or Crappie fished the lake, for that matter.
Most of the major launch ramps charge up to $10 to launch. And don't be surprised if you're a couple of boat lengths away from a main lake cliff bank & your electronics says it's 80ft deep, or out in the middle of the lake & it's reading over 150ft deep. Herrington Lake was made by damming up the Dix River, which was a class 3 rapids river that was used for transporting timber to the mill (around where Kennedy Bridge is located). It's basically a limestone canyon in the lower portion of the lake.
And if you're going to be there ON the 4th ... expect the local lake residents to be firing off all manner of fireworks from dusk, well into the night.