Sometimes prying personal information from famous actors is difficult, but ask Mark Ruffalo why he’s obsessed with clean water — the wellspring of his new movie Dark Waters — and his life story pours out.

“When I was a boy, my love was the creeks, the streams, the woods. That was my safe place, that’s where the mystery was. That’s where God was for me. I feel like I was an environmentalist early on,” said Ruffalo, 51, who grew up in the 1970s in Kenosha, Wis., on the shores of Lake Michigan, where as a lad he naturally became alarmed when anglers started pulling deformed fish from his favorite swimming holes.

“I’m asking my parents, why were the fish getting these problems? The answer: pollution. And of course my next question was why don’t they do something about it? Well, by God, they did. In the 14 years I lived there, they cleaned that lake up. That made a huge impression on me, about what was possible, and could be done,” said Ruffalo, who stars in Dark Waters and produced it as well, shepherding it from a magazine article to a major Hollywood release (distributed by Comcast’s Focus Features) in just three years.

It’s the true story of the problems that arose in Parkersburg, W.Va., where the water was contaminated by unregulated chemicals (PFOA, short for perfluorooctanoic acid, used in the production of Teflon) leaching into the water supply from a plant operated by Wilmington-based DuPont. (In the Small World Department: Ruffalo earned one of his three Oscar nominations in Foxcatcher for playing wrestler Dave Schultz, killed in 1996 by John du Pont, heir to the family company, in Chester County.)

Ruffalo felt like he knew the people in the story. Parkersburg, he believed, was not so different from Kenosha, a changing industrial town on the water, a place familiar with hard times but surrounded by natural beauty. The kind of natural beauty Ruffalo wanted for his own kids.

“I moved my family from Los Angeles to rural New York, because I wanted to give them that experience that I had. And of course, in all my wisdom, I end up moving them right into the middle of the gas lands, right at the peak of the fracking boom," he said.

As New York debated whether to allow hydraulic fracturing of shale, Ruffalo kept his eye on what was transpiring in nearby Pennsylvania. Through friends and neighbors, he became interested in the impact of fracking in places like Dimock, where he was invited by residents to check out their flaming water and bring attention to their situation.

“My first reaction is, you’ve got the wrong guy. I’m just an actor. What can I do? And their response is, well, we don’t know, but anything would be helpful,” said Ruffalo, who spent a sleepless night thinking about his next move. He knew the kind of blowback he’d get for trading on his celebrity and jumping into a politically charged issue.

He had come to New York looking for a peaceful life for his family — was this any way to achieve it?

“The question in my mind was, ‘Who are you?’" he said. "'Are you going to help people? Are you going to look out for the little guy? Are you willing to use your platform to get out there and help people, real people? They’re your neighbors and they’re asking for your help.'”

Ruffalo jumped in with both Hulk feet, going to not only Dimock, but Flint, Mich., and wherever else the water was on fire or poisoned with lead. (He volunteers with the Delaware River Watershed Initiative, and was in Cheltenham in 2016 to help clean up Tookany Creek.)

He’d been on the lookout for a project that could combine his acting and his activism, and when he read a New York Times Magazine article about Cincinnati lawyer Rob Bilott and his multiyear battle with Parkersburg residents against DuPont, he knew it was an ideal story for him.

So did everybody close to him.

“The day it came out, I had five friends call me and say, ‘This is perfect for you.’”

He decided to produce it himself, looping in Anne Hathaway, Tim Robbins, Bill Camp, and Bill Pullman. As director he hired Todd Haynes, who grasped the ambitious scope of the story Ruffalo wanted to tell in Dark Waters — lax regulation of PFOA and Teflon, so-called forever chemicals, but also the story of a blue-collar community and its conflicted relationship with a company that is both provider and polluter.

Ruffalo is proud of the way the film shows the complex calculations that people in towns like Parkersburg (or Kenosha) have to make when they try to determine what’s best for their families.

“They’re beholden to that company, it’s their livelihood and there’s an allegiance to it. You have people who realize they have to make this choice between their lives, and something that is vital to the life force of the community.” Ruffalo said.

The story starts in 1999 with Bilott taking the case of a farmer (Camp) who suspects his cows are being poisoned by something emanating from a nearby DuPont landfill, and though the farmer’s suspicions are justified (confirmed by a lawsuit and material uncovered in discovery motions), the farmer nonetheless becomes an outcast in a town full of DuPont workers.

Ruffalo’s character has trouble in his own white-shoe law firm (whose clients are usually corporate defendants, not plaintiffs), which devotes considerable resources to the case and for years gets little in return — the outcome of the case against DuPont rests on a court-ordered scientific and epidemiological study of Parkersburg that took the better part of a decade.

Bilott eventually prevails (after a near-breakdown), but additional plaintiffs suffer and die and the facts unearthed about PFOA (DuPont calls it C8) are dispiriting — in 2011 the scientists reported a ‘‘probable link’’ between PFOA and kidney cancer, testicular cancer, thyroid disease, high cholesterol, preeclampsia and ulcerative colitis. More than 70,000 people were exposed.

So there is vindication, but no celebration.

“As time goes on in America and our working class gets squeezed and our unions disappear, and our elected officials become more and more timid, the pickings are slim, and people have fewer and fewer places to go for good jobs, and for justice,” Ruffalo said.

Ruffalo found himself in front of elected officials this week when he testified before Congress about Dark Waters and what it has to say about PFOA.

A representative “came at me,” he said, with an assertion that the movie misrepresents the effects of the chemicals.

No way, said Ruffalo. Lawyers pored over every script detail — the same crew that vetted one of his other recent muckrakers — Spotlight, about sexual abuse in the Catholic Church.

“I know that I get labeled as a political activist, but I really try to frame things in a way that won’t get politicized. You ask me why I’m interested in clean water? That’s why. Because that shouldn’t be political, and it isn’t, really. It’s something that everyone can agree on. We all want clean water, for ourselves and for our kids.”