Turtles

This is probably a Yellow-bellied slider (Trachemys scripta scripta)--we'd need to see the belly to be sure. This turtle is not originally native to this area. It's a very common turtle from Virginia down into Florida. It's commonly kept as a pet, so it's possible that this one was released. They have been reported from Montgomery and Philadelphia counties in recent years https://paherpsurvey.org/taxon.php?taxon=630. 

Please be sure to leave turtles and other wildlife where you find it along the creek. A turtle like this might live for 30 years or more.