D.B.
Your local DNR might be helpful in identifying what species it was. The good news for you is that there are only 3 venemous snakes in PA - 2 rattlers and the copperhead. None would be found by or heading into water. Possible it could have been a hognose, as they like to eat frogs. Most likely, though, it was a Northern Water Snake. NOT to be confused with the Cottonmouth which is not found in PA. Harmless unless you area fish or frog or if you corner it and it's trying to defend itself. The younger ones are lighter in color.
As with all snakes, they are all around us. They like to go unnoticed and fulfill a very important function in the ecosystem. They will always try to get away from a human or anything larger than them. They aren't dumb and don't seek out fights! Don't have many vermin around your property? You can probably than a black rat snake for keeping the population in check. And if he lives his life the way he wants to, you'll never see him unless you go poking for him.