Comedian Harry Shearer directed and serves as onscreen narrator for this absorbing documentary, which exposes the human failure that surrounded the flooding of New Orleans during Hurricane Katrina. The suffering of New Orleanians having been adequately covered in other documentaries, Shearer sticks to the physical record of what happened, using graphics to map out the city and its waterways and interviewing mostly engineers and academics who know how the system was conceived and why it collapsed. The Army Corps of Engineers emerges as the major culprit—Karen Durham-Aguilera, the corps’ spokesperson for the movie, agrees to talk only about the future of the region—though there’s plenty of blame to go around once Shearer takes up the Mississippi River–Gulf Outlet Canal (“Mr. Go”), a huge federal pork-barrel project that wound up feeding the storm waters into Greater New Orleans. Shearer is no Spike Lee—the movie tends toward the episodic, with section titles set to canned jazz and lame cameos by John Goodman of Treme—but he deserves credit for moving past the heartbreak and outrage in search of long overdue answers.