Oldwolf,
My family has a camp on Sebec Lake, about an hour from Rip. Dam. I have fished it during all three seasons, and in Mid-Sept, the salmon hit incredibly. I would fish a yellow marabou streamer in size 6 or 8 over any other fly this time of year. A close second would be the light edson tiger marabou in the same sizes. There will be a lot of fishermen there at that time, but there is a lot of water, too.
Trout