As I said in the first post about my trip last week, The Hudson really changes above Troy. Not only does it become a river rather than an estuary but navigation become more difficult and then as you head further north impossible due to the elevation drop. Once you reach Hudson Falls you find a string of five waterfalls within 20 or so miles of each other. Four of these are deeply industrialized, one is pristine. Most people have heard about the massive ongoing PCB cleanup. The PCB in the river came from two GE plants, one just below Hudson Falls.
Map from Lock 5 to Rockwell Falls in the town of Hadley NY