A crestliner with 150!! I saw two huge boats put in at the marina. One took nine aboard! By your report, Plmlk, you were between Waterford and Rochester dams.
Playing detective, I would say one of two ways to launch:
1. They own or know someone who lives along the river and put it on private property.
2. There used to be a launch on the canal, on private property. A few years ago I looked and it was still there. Either condos or apartments next door.
Otherwise, I have no clue how such a large boat put in between the dams. By the way, nice catch for this time of year.