Yes, Osama bin Ladin roams free, but our crack national security apparatus is right on top of serious threats like this:

On July 25, Jim Bensman of Alton, Ill., attended a public meeting on the proposed construction of a bypass channel for fish at a dam on the Mississippi River. Less than a week later, he was under investigation by the F.B.I. — the victim, depending on how you look at it, of either a comedy of errors or alarming antiterror zeal.

The meeting was organized by the Army Corps of Engineers, which maintains Mississippi River navigation systems, including the Melvin Price Lock and Dam in East Alton, Ill., where it is considering construction of a fish passage.

At the meeting, Mr. Bensman, a coordinator with Heartwood, an environmental organization, suggested the corps simply destroy the dam. It was an idea the corps itself had considered. In fact, a photograph of an exploding dam was included in the corps’ PowerPoint presentation, explosive demolition being by far the most common method of dam removal.

Mr. Bensman said he had long criticized the system of locks and dams as environmentally damaging and an unfair government subsidy benefiting boat traffic over railroads. “I’ve been fighting these things for decades,” he said.

But news accounts of the hearing did not put it quite like that. One newspaper said simply that he “would like to see the dam blown up.”

And on July 31, he said, he got a telephone call from someone who identified himself as Matt Federhofer, an agent of the Federal Bureau of Investigation. There is such a person at the agency’s office in Fairview Heights, Ill., a St. Louis suburb, but he did not respond to a voicemail message yesterday. .

When Mr. Bensman learned what the call was about “it was just kind of disbelief,” he said. “How could anyone be so utterly stupid as to think that was a terrorist threat?” For one thing, he said, it would be ridiculous for a would-be terrorist to announce explosive intentions at a public meeting, much less a meeting sponsored by an arm of the military.

But when the agent said he wanted to visit him at home, Mr. Bensman became frightened. “I was thinking, I need to talk to an attorney,” Mr. Bensman recalled. “And he said, ‘Well, O.K., I will put you down as not cooperating.’ ”

That was when Mr. Bensman got angry. “I know what Bush is doing with all these secret programs spying on the so-called terrorists, all these provisions in the Patriot Act that I think crosses the line, being able to spy on a suspected terrorist without the check and balance of a court or a judge,” he said. “That’s just something that really worries you.”

He said he also remembered that the F.B.I. had a history of spying on civil rights, antiwar and environmental activists. He said one reason he knew his caller was a genuine agent was that he could cite items in Mr. Bensman’s own F.B.I. file.