I believe they are able to reproduce on their own in many of the rivers. If looking for a meal, then might want to check the PFBC advisories of which river to check out. For catching walleye and not for consumption, the Allegheny below just about any of the lock and dams closer to Pgh (doesn't have to be directly below, but within a mile), should get you into fish. Especially when the water cools a bit. Mornings and evenings usually have a few hour window where you can catch them pretty consistently. I haven't done it for a few years, but reports that I have read in that time seem to be the same. Some guys on here can get them biting pretty much year round, but I always did best in the spring or fall evenings.
Any other inland lake in PA, for me at least, they are a nice bi-catch. Any time that I focus on them, I spend hours of maybe a bite here or there. If extremely lucky, I end up with one. About 25-30 hours of trolling for every fish, is about my walleye success rate at Arthur. Obviously, some have a much better rate. Others likely worse.