I fly there at the water works and boathouse all the time and sometimes I would see police helicopters and security guards at the park but they are not saying anything to me to indicate that it's illegal to fly there, so I'm guessing it's ok to fly there. The only no fly zone I know in Philly is flying over stadiums even if there is no ongoing game we are not allowed to fly over stadiums for some reason. Here's couple pictures from the water works.