Enviros and river lovers are celebrating the remarkable recovery of the Blackstone River in Rhode Island, the result of a 30-year grassroots effort to clean up what locals once dubbed the Black Hole of the Northeast. The river, lined by many industrial revolution-era mills, had suffered from more than 200 years of pollution and was choked with old tires, appliances, and cars. “When I was a child, you would not go near the Blackstone for any reason. It was awful to look at,” said Robert Billington, president of the local Blackstone Valley Tourism Council. Over the past three decades, volunteers hauled away tons of trash from the river, more than two dozen dams were brought down, and the number of fish species rose to 36 from only two. New parks have been built along the river’s banks, old mills are being converted into housing, and plans are in the works for riverside hotels and eateries. There are plenty more problems to be tackled — stormwater runoff, sewage drainage, toxic sediments. But Blackstone boosters are encouraged enough to aim for making the river safe for fishing and swimming by 2015 — a goal that would have been inconceivable a few decades ago.