Environmental officials say they have learned through trial and error that it can be far more effective to take an entire river system into account, rather than proceeding piecemeal. For example, this idyllic-looking stretch of waterfront in Lyndhurst is just a tiny part of the Passaic River Diamond Alkali Superfund site, which now also includes all of Newark Bay and the lower 17 miles of the river. Planning and cleanup work is going on elsewhere on the Passaic, but officials hope that addressing this hot spot with innovative technology now could speed the entire project.

Under the Superfund’s “polluter pays” approach, companies that are responsible for the pollution can be forced to pay for the cleanup. But with rivers like the Passaic, which has been used by hundreds of businesses to dump industrial wastes for more than two centuries, identifying those responsible can be a legal nightmare. According to the E.P.A., more than 70 businesses will have to pay for the Passaic cleanup, which could cost more than $3 billion.

In June, the agency reached an agreement with dozens of private companies to pay for removing 16,000 cubic feet of heavily contaminated sediment from the Lyndhurst hot spot. The area will then be capped and monitored until the agency selects a final cleanup plan for the entire stretch.

On top of the legal difficulties of this project, the Passaic is actually a tidal tributary of New York Harbor, meaning that there are two-way tides and a mixture of saltwater and freshwater that propel pollution both ways for miles. And because the Passaic presents a major flood hazard, any possible solutions must not impede the river’s flow.

A Shaky Start

Part of the E.P.A.’s reluctance to dive into river cleanups can be explained by the Superfund program’s difficult beginnings. As it got under way in 1981, it faced strong opposition from Republicans in Congress and the administration of President Ronald Reagan. When the program finally came up to speed during the Clinton administration, the priority was on upland sites, with rivers all but forgotten.

“It was discussed at the beginning, but clearly it was not the initial priority,” said James J. Florio, the former New Jersey governor who as a member of Congress was the principal sponsor of the Superfund legislation. River cleanups, he said, are “very complicated and very difficult, with the possibility that dredging makes things worse.”