A wayward dolphin that meandered into a polluted urban canal, riveting onlookers as it splashed around in the filthy water and shook black gunk from its snout, died Friday evening, marine experts said. The deep-freeze weather hadn’t seemed to faze the dolphin as it swam in the Gowanus Canal, which runs 1.5 miles through a narrow industrial zone near some of Brooklyn’s wealthiest neighborhoods. … The filthy canal was named a Superfund site in 2010, meaning the government can force polluters to pay for its restoration. For more than a century before, coal yards, chemical factories and fuel refineries on...