Right in Fairmont Park is the Wissahixon for a quick fix. At lot of Philly guys hit the Lehigh Valley limestoners (Little Lehigh, Saucon, Monacacy, Bushkill, Cedar etc) or ones a little closer like Valley or Cook's Ck. Little limestoners dot PA Dutch country. Most have real sediment problems, but a handful are being brought back to life. The Poconos is a little farther with the Bushkill, Tobyhanna, Lehigh, Brodhead, and Pohopoco (a tail water) being popular.
Basically you need to go to the Mountains or a limestoner to find cool water.
Charlie Meck's guides for PA are usually good. Check out Pennsylvania Fish & Boat Commission site for lots of info.