Stenonema,
I'm not exactly sure how to take your post. Just because I fished twice with a person that shall remain nameless doesn't mean I'm that person. I've never had a problem posting photos or general info on waters that I fish. Sharing some info with public is OK in my book.
Back to the OP........ It's not a stretch that there are resident trout in the Susky (even as far south as the York Co line or even lower). There are also transient fish that find thermal refuge during warm water periods. Good luck finding these populations though. Just think of how many wild trout streams and stocked streams dump directly into the Susky. Over a 50 year period, some of those fish have been blown into the river or moved there of their own free will. Most would perish but some adapt. It took the bows on the Delaware less than 100 years to morph into their own unique strain. Able to withstand warm temps and highly migratory. Why couldn't the same exist on the Susky, Pine, Lehigh, Juniata, Swattie and countless other 'warm water' rivers? Very interesting, small population numbers and elusive.
Last winter, I had a long talk with Clouser Sr about trout in the river. He did tell me that he's aware of 2 very large springs in the main river. He's had clients bass fishing and spotted browns cruising the edges of the cool water. He told me he saw a large shape moving through the weeds and assumed it was a big carp. As it got closer to the boat he got a better look and said out loud 'what the hell is an Atlantic Salmon doing in this river?'. He'd seen them in and around the springs for years (but only at specific times of the year). He never targeted them either. Pretty cool. I'm positive I found a pod of bows feeding on Sulphurs one spring and they let me get my boat quite close. I only had a 7wt sink tip with me so I just observed for a while and moved on. I've heard of big bows in Susky above Williamsport and in the W Br of Susky. I imagine the populations are so small and spaced out that it's never warranted any interest from PFBC for a study. The fish in the original pic has to be 12-15 years old! Snap a pic and get him back in the water. At any rate, just fish because you never know......you might just find one of these unicorns.