People won’t stop fishing in the extremely polluted Gowanus Canal, so the EPA, sensing a public health hazard, made it a superfund site. And on Thursday, the agency announced it was going to cost $467 million to $504 million to clean it up. It’s going to take until 2020 and will require dredging the whole canal, where heavy metals line the bottom and sewage still flows. A massive project, to be sure, but it should hopefully pay off in a better-smelling neighborhood with fewer toxic fish in circulation.