Humorist Harry Shearer gets serious in his new documentary, “The Big Uneasy.”

Most widely known for his work on “The Simpsons” (providing the voices of Mr. Burns, Ned Flanders and several other characters) and for his on-screen roles in a number of “mockumentaries” with Christopher Guest and Michael McKean (including “This Is Spinal Tap” and “A Mighty Wind”), Shearer, 67, is also a part-time resident of New Orleans, which was devastated by Hurricane Katrina in 2005.

In large part, Shearer says, the news media reported on the resulting flooding of the city as the aftermath of a “natural disaster,” but “The Big Uneasy” -- which he wrote, directed and hosts -- posits that much of the tragedy could have been prevented, chalking up the failure of the city’s levee system to “man-made errors in judgment, design and construction” by the U.S. Army Corps of Engineers.

On Monday night, Shearer will attend a special screening of the film at the Lefont Sandy Springs Theater. It's a benefit for the Upper Chattahoochee Riverkeeper organization, and the $15 tickets also include a pre-screening reception and a post-screening audience discussion with Shearer. (An additional regular showing of the movie is scheduled for 1 p.m. Thursday.)

Q: What motivated you to make “The Big Uneasy”?

A: In the weeks and months after the flooding, thanks to our local media, those of us living in New Orleans were getting reports about the interim findings and ultimately final conclusions of two independent investigations into why the city flooded. But the national media was reporting on it as a natural disaster. Blogging about that misinformation [in his columns for The Huffington Post] wasn’t enough, so this documentary seemed like the best way to try closing the gap between what we knew and what the rest of the country was being told.

Q: What did you think about any of the earlier documentaries on the subject [the Oscar-nominated “Trouble the Water” and director Spike Lee’s “When the Levees Broke” and “If God Is Willing and Da Creek Don’t Rise” for HBO]?

A: The “why” was missing. Isn’t that supposed to be one of the five W's in journalism? No one seemed to be interested in talking about that, or even thought there was a “why.” Ignoring that, though, is essentially like pushing the snooze button on a story that should’ve been a wake-up call. There are more than 100 cities in the country that are facing the same potential problems with their levee systems, but the Corps of Engineers is basically pretending that the problem doesn’t exist. Their mantra is about looking ahead, not looking backwards, so there’s this full-speed-ahead attitude, and “The Big Uneasy” is sort of like a little fly buzzing around their bountiful picnic.

Q: Ideally, what do you hope to achieve with the film?

A: To pressure Congress and the executive branch to stop dealing with 21st-century problems in a 19th-century way, to pay more attention to people in other parts of the world, like the Dutch, who’ve already learned what we haven’t, to change how the corps does business. There are new and different methods of dealing with these issues, but the corps is very set in its ways. And why not? They never seem to get punished for any of their shortsightedness.

Q: You’ve directed regular features before. How did making this documentary challenge or reward you differently?

A: In one sense, making a film is making a film, with a lot of the same frustrations and satisfactions. Working with real people as opposed to professional actors, my main job was to make them feel comfortable and relaxed, so that the conversation felt as natural as possible. Unlike working on a scripted project, once we got into the editing room, we had a much bigger batch of material from which to sculpt the film. It’s not about me spouting my own personal opinions. It’s about letting these other people tell their own stories.

Special screening

“The Big Uneasy”

7 p.m. Monday. Lefont Sandy Springs Theater, 100 Sandy Springs Circle N.E., Atlanta (lower level of Parkside Shopping Center). $15, including a 6 p.m. pre-screening reception and a post-screening Q&A. 404-255-0140, lefonttheaters.com.