In the middle of Brooklyn, a narrow, 1.7-mile canal is staging one of New York's more entertaining identity crises. Glass-walled condos and exposed-brick lofts now crowd its banks. On weekends, the sidewalks fill with people clutching natural wine and looking for the gallery opening. Real estate brokers will tell you, with a straight face, that this is one of the hottest neighborhoods in Brooklyn. And yet six to fifteen feet beneath all that hipness sits a century and a half of industrial sediment, settled into the canal bed like a fossil record nobody asked to dig up. The Gowanus Canal is currently living two timelines at once, and they do not agree with each other. How a Canal Becomes a Sewer The Gowanus didn't start out as a natural waterway — it never had the luxury of being romantic. In 1869, New York City dug it out of marshland specifically to move freight into inland Brooklyn. Coal, lumber, and manufactured goods flowed through it, and the canal quickly attracted exact...