things got considerably worse.

In 1990, the Environmental Protection Agency, or EPA, designated the Blackstone as the most polluted river in the United States.

But unlike the visible debris of the past, that distinction came from the unseen pollutants.

- Things that we're still working on today are other pollutants in the water that shouldn't be there.

- [John] Jane Sawyers is a supervising environmental scientist at the Rhode Island Department of Environmental Management, or DEM for short.

- So it's the metals, it's bacteria, it's other pollutants that are on the waterway.

It can even be just sediment itself.

- [John] And the contamination wasn't just from the Blackstone's industrial past, the river was getting a fresh supply of sewage from poorly regulated treatment facilities.

- The Blackstone River and other rivers were seen as conveyances.

That's where you put your waste.

And it could be that you knew what the factory upstream was doing because of the color of the water today was this color.

So that's not gonna be healthy for the fish, it's not gonna be something people want to recreate in.

- [John] At the Woonsocket Wastewater plant, those efforts are evident.

Here, sewage is treated through a 10-step process before as much as 7 million gallons goes into the Blackstone every day.

- We issue permits to the wastewater treatment facilities.

We've continually worked on those with the regulated community, and as we've moved those permit limits down and the treatment plants have been able to build and remove some further pollutants from the water body.

That permitting effort has continued to keep the Blackstone clean, and it allows the fish and the aquatic life to thrive in the water.

- Now, the Rhode Island DEM is investigating the discharge of partly treated sewage wastewater from a Woonsocket treatment plant facility on Cumberland Hill road.

- [John] But there still have been problems at this site, although it has been reported that they have been addressed.

The plant declined to comment.

For Sawyers and others, however, sewage isn't the only source of contamination to worry about.

- Stormwater is a big problem.

Sidewalks, parking lots, rooftops, they're not going to hold and trap the water.

So they're gonna move everything directly into the water body.

It's not gonna infiltrate and remove those pollutants.

- [John] And she says, one of the greatest issues with storm water comes from our front yards.

- The same nutrients that we use to fertilize our lawns that are in pet waste, human waste, they can feed algae and aquatic plants and they can overgrow.

And that's not easy to recreate in, it's not easy for the aquatic life to live in.

And if that dies off, it can really drop the dissolved oxygen levels.

You could have a fish kill, you could have other kind of aquatic life not living.

- [John] To ensure specific water quality standards are met, the Department of Environmental Management adheres to a rigorous schedule of sample collection and reporting.

- We test for bacteria, we test for metal, we compare it to our water quality regulations and decide whether or not the waters are meeting our regulations and our goals.

And if they are, then that's great, and if they're not, if they have some kind of pollution in them, we put them on a list that we report to EPA and to the public.

- [John] Sawyers says that while many contaminants have been added to the list, recent testing has yielded some successes.

- Some of the pollutants that were an issue that we've been working on for decades, we're able to start to take those off the list, the data showing that we are meeting our goals for those pollutants, and that's very exciting news.

- [John] Over the past two testing cycles, pollutants such as total phosphorus, dissolved oxygen, and dissolved lead have all been removed from the EPA's list.

But while progress has been made in addressing known pollutants, a new challenge is emerging.

First introduced in the 1940s, forever chemicals, otherwise known as PFAS have been used in many consumer and industrial products including food packaging, water repellents, and cosmetics.

According to the EPA, they contaminate soil, water, air and aquatic life around the globe.

And studies have shown that these chemicals are even found in most human bloodstreams.

- There's a lot of challenges with testing for PFAS, and it's cutting edge research.

EPA has a roadmap to try to walk through those steps of how do you even collect a sample?

PFAS is in everything, it's in people, so how do you collect a sample without contaminating that sample?

- [John] Although PFAS present new challenges, Sawyer says she and others still have their eyes on the same prize as the pioneering Project Zap volunteers 50 years ago.

- To see the progress that people are making is very exciting.

In the original Operation Zap Blackstone, they had to rally support to get this going, and they were able to get a whole huge community going.

And I think that has just kept going.

50 years later, the new generation of people are coming on board.

- Zap Blackstone.

- That's our broadcast this evening.