“I don’t think so,” he said. A minute later, as if on cue, a three-foot chunk of rotten wooden piling crumpled into the canal with a splash.

The 2010 addition of the Gowanus to the federal Superfund list of the nation’s worst hazardous waste sites followed more than a century of insult and injury at the hands of gas plants, chemical makers and tanneries.

It took another six years for work to begin. Last fall, in a test area behind Whole Foods known as the Fourth Street Basin, contractors fished out the first debris: the 63-foot hulk of a former ferry where artists held exhibitions and parties in the canal’s wilder days. Now they are dredging the basin to scoop up 10 feet of black sediment heavily laced with coal tar.

The cleanup of all 1.8 miles of the canal, overseen by the government but paid for by polluters and the current owners of their properties, could take about 10 years, officials said. (The cleanup has already weathered one funding scare under President Trump. But his E.P.A. chief, Scott Pruitt, has said that running Superfund cleanups is one of few things the agency should be doing.)

The canal’s health is getting a big boost from the city, too. For example, a pair of huge underground holding tanks are expected to reduce the flow of raw sewage into the canal to a relative trickle of 11 million gallons a year, down from the present 26 million gallons.

One sewage tank is to be built beneath a gravel lot where the city now stores road salt in a giant shed. It is here that the Gowanus Canal Conservancy hopes to build an education center at the hub of what it calls “N.Y.C.’s next great park,” a network of oases strung one after another on both banks of the canal.

The conservancy’s Gowanus Lowlands manifesto conjures a dreamscape of sloping grassy knolls, maritime meadows, performance spaces and picnic spots. The reality will probably be a bit different, but the city has said it will push developers to create varied ways to enjoy the waterfront, beyond the paved walkways and benches behind Whole Foods and the Bond Street high-rises.