Cullen Hoback, who directed “Terms and Conditions May Apply,” the eye-opening documentary about how corporations mine data from your cell phone and internet use, obviously has a nose for investigative journalism. This time, he followed his investigative instincts to West Virginia, where he sniffed out a mystery surrounding a community’s tainted water system. His surprising discoveries are revealed in his new film “What Lies Upstream,” which will open the Slamdance Film Festival on Friday.

In 2014, West Virginia citizens living near the Elk River began to complain that their tap water had a funny smell. But they were unable to get any answers from the likely culprits — a string of nearby chemical plants perched along the riverbanks.

Hoback’s mom was the first to tip him off, and while he had long since moved away, he remembered spending childhood summers playing in the West Virginia woods.

“It struck a chord. I it wasn’t hard for me to imagine myself in that position, the uncertainty of not knowing what had happened to my water and what would happen to me,” he said.

Hoback’s initial sleuthing turned into a complicated three-and-a-half-year investigation that eventually implicated the federal agencies supposedly responsible for regulating water and environmental quality.

Did he expect that?

“Certainly not. In the beginning, I thought I was making a film that was just an investigation into this spill in West Virginia. Then, as the project progressed, it became clear to me it was about much more. I didn’t know, really, that it went all the way up to the federal level until I connected all the dots in Flint,” he said.

As it happened, while Hoback was splashing around in the river collecting water samples in West Virginia, the national media was just beginning to report on a similar story in Flint, Michigan, where lead had leached into the city water system. Hoback went there to see if there were any parallels.

In Michigan, Hoback interviewed Marc Edwards, a Virginia Tech environmental engineer who was helping to lead the water investigation in Flint.

“I still thought the EPA and the CDC were the good guys … and he had to tell me three or four times, maybe more, that it was actually coming from within the organizations themselves, that the corruption was inherent. That blew my mind,” said Hoback.

Back in West Virginia Hoback began to question lawmakers at the statehouse with a deeper sense of skepticism about their claims the water was safe to drink.

The findings from his own water samples, collected during an after-dark river expedition in below-freezing temperatures, were disconcerting. Under persistent on-camera questioning Hoback learns that elected officials had minimized the health hazards, the plants had not undergone required inspections and no one seemed to have adequate data about the long-term effect of the tainted water on West Virginia’s residents.

While making the film, Hoback said he encountered resistance, not only from the chemical corporations, but even more so from government agencies.

“The security at the chemical companies was small potatoes. While we were filming outside of the CDC, on public property, an armada of vehicles came out and surrounded us. Their security force actually demanded my footage. I told them I had a legal right to keep it and they eventually agreed. Had I not known my rights in that situation they would have intimidated the footage right out of my hands,” he said.

Hoback is concerned that regulatory agencies will become even more opaque under the new administration currently being installed in Washington, D.C. As the implications of November’s election sank in, Hoback realized he had to revise his film.

“On the night of the election, one of the things that crossed my mind, almost immediately was that I had to re-edit the film. I spent the next month re-editing to deal with this new reality — where science would be headed under a Trump administration.”

While gravely concerned, Hoback said he still maintains some hope that science will win out. And he hopes his film and other documentaries like it will help.

“I don’t know how you will feel when you finish this film, but when I finish a really good documentary it opens my eyes. It leaves me with this emotional resonance that lasts for a long time, it makes me want to do something.”

Hoback added, “I think documentarians right now have never been more important, and I hope the messages they share will really make a difference.”

The Slamdance documentary film “What Lies Upstream “ will screen at the Treasure Mountain Inn:
Friday, Jan. 20 at 6:45 p.m.
Monday, Jan. 23 at 3 p.m.