Perelman Park appears to have limited to no habitat for adult bass. There are areas of much better bass habitat in other areas between Lancaster and Hinkletown/Martindale area. Add to that the very lower stretch of Cocalico Ck.
Conditions appear to worsen below Lancaster, although there are isolated stretches of good bass habitat in places down there. I have found one or two in a couple of hours of searching. However, the good habitat stretches down there are short and the the stream then returns to degraded conditions of gravel, silt, and sand with little bottom structure in the stretches that I have checked. Others probably have much more experience with that stretch than I do.