Stretching 315 miles north from New York Harbor to its source in the Adirondacks, the majestic Hudson River became a major trade artery with the opening of the Erie Canal in 1825, which connected it to the Great Lakes at Buffalo. But patterns of commerce changed and by the early 20th century the Hudson Valley had fallen into decline. Fortunately, the past few years have seen a renewal spurred by relatively inexpensive real estate, a revived agricultural base and the appeal of the river itself, now cleansed of industrial pollution.