From the River Journal Blog
You might not realize it, but the trail that slices through many of these river towns sits atop a rich vein of history. Just below the surface lies the Old Croton Aqueduct, one of the engineering marvels of the 19th century. It’s no exaggeration to say that New York City’s explosive growth would have been impossible without this gravity-fed tunnel, completed in 1842. Before the Aqueduct, water in the city was so scarce and foul that cholera raged, fires burned unchecked, and the safest quaff was beer. All that changed when fresh water started flowing through a 41-mile brick-lined masonry tunnel from the Croton Dam to a reservoir on 42d Street (now the site of the main city library).