The Hudson River is not an ordinary river. Rather, it is an estuary, where salt water from the ocean mixes with freshwater for 153 miles, from New York Harbor to Troy, NY. During the 1950s, the Hudson was an open sewer, with industries discharging toxic chemicals, paints, heavy metals and other waste into the water. Fish were contaminated with PCBs (polychlorinated biphenyls) dumped from General Electric’s factories into the upper Hudson, and more than a century of dredging and filling devastated its ecosystems.