Harry Shearer is a mockumentarian, not a documentarian. But the constant depiction of Hurricane Katrina of a natural disaster finally set him off last year after half a decade of trying to promote the idea that the 2005 flooding of New Orleans had deeper roots than a weather event. Spinal Tap fans know Shearer best as the hirsute bassist Derek Smalls and the other roles he’s played in the Christopher Guest corpus; far more know his many voices on The Simpsons—Ned Flanders, C. Montgomery Burns, Seymour Skinner, and about a thousand others. But Shearer isn’t joking around with The Big Uneasy. In the film Shearer gives new attention to an investigation of how the levees really broke, and the assessment is stark. Decades of make-work government contracts and entrenched bureaucracy in the form of the U.S. Army Corps of Engineers flooded New Orleans, Shearer’s film argues. And the vital lessons of Katrina may have gone unlearned. The Big Uneasy, which premiered last August, screens tomorrow at the DC International Film Festival. We spoke by phone yesterday.

You make the case that what happened in New Orleans wasn’t a natural disaster but a failure of engineering. What compelled you to put this argument in a film?

As a New Orleans resident I’d been hearing these reports coming from these investigations and I’d been doing interviews with the people in the movie on my radio show and blogging about it on The Huffington Post. When President Obama came to New Orleans in October 2009 and called the flooding a natural disaster my head hit the ceiling. One does feel this is a smart guy. The failure of the federal government to prevent the flooding was one of the events that made him president so one would hope that’s on his radar. He stands in the middle of the city and says brazenly what we know not to be true. I decided radio and blogging aren’t enough, so why not make a documentary? I asked for a show of hands, and being the only one in the room mine was the only hand that went up.

Sounds like things haven’t changed that much.

As far as New Orleans is concerned things haven’t really changed and hope is in the eye of the beholder. The story is over four decades under various administrations. It could almost make you non-political.

You lay the fault with the Army Corps of Engineers, and you suggest they’re making the same mistakes again. Is it, for lack of a better phrase, bureaucratic complacency?

It’s bureaucratic complacency inside the Army Corps of Engineers. Let’s call it what it really is. There was a phrase used by an American diplomat about the corruption in Afghanistan: culture of impunity. That’s what we have here. No one got punished for failing in a way that killed over 2,000 people. They got promoted. They got more money for a new project that has the same problems. That’s more than complacency. It’s not just in New Orleans. The same story is being played out all over the country where levees are breaking. New Orleans is the canary in the coalmine. So if you’re in Sacramento or Dallas, look out, it’s coming your way.

You’re not originally from New Orleans. Why did you move there?

I started going to New Orleans as a visitor in 1988 and immediately fell in love with the place. My wife and I bought a place there in the late ’90s and have been going there more and more ever since. I consider it my primary home now. You can focus on the really amazing food and music and architecture, you can take all that away and it’s still an amazing place to be because of the people. There’s a culture there. And that’s what’s sort of always seductive about the place. They have a different understanding of what life’s about. A friend of mine said “It’s a city that doesn’t live by the dollar or the clock.” But let’s be honest, there’s no place that’s great to live if you’re horribly poor and obviously there’s lots of poverty there.

A lot of your argument is also with how the flooding was covered.

The media narrative was this was a natural disaster in city below sea level that affected mostly poor black people. The reality is this was a man-made disaster that flooded 80 percent of a metropolitan area and 100 percent of a suburban county. It’s 50 percent above sea level. It affected poor black people, poor white people, rich white people, rich black people, everybody. It was a citywide, culturally diverse, economically diverse catastrophe. And it got marginalized by the national media into this much more limited idea of what this event was. I think that affected the level of political will to change things.

So how are things today?

I think New Orleans has been extremely lucky in the last few years in that there hasn’t been a weather event that has challenged the system that is currently in place. Me personally? I hope our luck holds up. I don’t have the level of confidence I would like to have in the protection we have been given. There’s not sufficient outside oversight of the Corps of Engineers. They’re much better at saying, “we’ve learned our lesson,” than actually learning their lesson. We talk about the canal known as “Mr. Go” (the Mississippi River-Gulf Outlet canal) that did incredible environmental damage. You can’t stop these people with a stick. Michael Grunwald (who investigated this topic for The Washington Post) talked about this iron triangle between the Corps, special interests, and congresspeople. It’s cozy and sometimes a few thousand people get killed. What happened in 2005 should have been a wake up call. We hit the snooze button instead.

How, then, do you get their attention?

I would love to get the attention of the current occupants of the White House. We’re going to be releasing a letter from the whistleblower in the film addressed to the president. It’s a personal that letter with information about the only response from the White House during her four-year experience trying to address this. It was not pretty.

What is the ideal response?

There are people who would like to reform the Corps of Engineers. I wish them all the luck in the world. I’m a filmmaker; I went to the people who know what they’re talking about. They paint a picture of an agency that is best described as rogue. If I could write the script for the president, I’d say issues of climate and water are going to be front and center. We have 21st century problems and 19th century solutions. We’ve got to go to the people who have centuries of experience in protecting people in low-lying areas—like the Dutch—and get rid of the American sense that we have nothing to learn from anyone else, because in this area we sure do.

The idea that we have nothing to learn from anyone else, that’s not exactly the most popular sentiment these days.

I know, but how many cities have to be destroyed before we start dealing with these problems? I don’t see cities in Holland going through what New Orleans had to go through. I remember seeing photos of flood control in Holland, in Britain where they built the Thames Barrier, then in New Orleans where the levees looked like they were built by a 3-year-old.

How much can be undone?

You’ll never fill in Mr. Go. They moved more earth than to build the Panama Canal. You can never heal the gash that has been made in the environment. You can close it off so it’s no longer a funnel. But some of this damage is for keeps.

So who is taking responsibility for New Orleans?

Both senators are very good advocates for what they think the state needs. Mary Landreiu and David Vitter, whatever one thinks of their other positions, have been very good in advocating for Louisiana. There are a lot of competing claims on federal attention and federal money.

I wanted to touch quickly on a completely different topic. You host a public-radio show (Le Show on KCRW in Santa Monica, Calif.). Do you have a take on the current attempts by Congress to defund public broadcasting?

It’s an attempt to defund NPR and PBS. Here’s what I can say. If you look back, NPR was every bit as bad during the run-up to the Iraq War as The New York Times and Washington Post were, but the Times and Post apologized, NPR didn’t. NPR was as bad with the New Orleans story. I think there’s something really wrong there, and I’m not sure I want my tax money going there until they figure out what the deal is. I think NPR has an inflated sense of its value. I live in London part of the time so I get to see the BBC. And anyone who thinks NPR is as good as the BBC is kidding themselves.

The Big Uneasy screens Saturday, 6 p.m. at GALA Hispanic Theatre, 3333 14th St. NW. $10. (202) 717-0700.

Shearer will be speaking at a DC Independent Film Festival “Master Class” Saturday, 1 p.m., also at the GALA Hispanic Theatre. $20-25.