JEFFERSON CITY, Mo. -- An underwater security system has been installed at the Lake of the Ozarks near Bagnell Dam to guard against potential terrorist attacks.

A half-mile string of buoys, installed in recent weeks, provide the surface evidence of the underwater barrier, which officials are declining to describe.

Osage Power Plant Manager Dan Jarvis said nothing would be able to penetrate the security barrier.

Utility company AmerenUE, which operates the hydroelectric power plant, has brought in 24-hour security personnel since the Sept. 11 attacks and installed high-intensity lights at the 70-year-old dam.

"We had an assessment of vulnerability of the dam by outside experts," Jarvis said. "Security is always a concern. It varies depending on the threat."

The utility declined to reveal the cost of the security upgrades.

The new security measures at the lake help protect the dam's eight concrete 50-ton turbines, which put out electricity for 3 percent of AmerenUE's 1.2 million customers in Missouri and Illinois.

AmerenUE also owns a nuclear power plant near Fulton, which was placed on a heightened state of alert after Sept. 11.

A difficult target

Tim Daniel, Gov. Bob Holden's homeland security adviser, said that while he supports security assessments at all major dams, attacks against dams would be a difficult task.

"It would take quite a bit of explosives, expertly placed to get at a dam," Daniel said. "I don't see anything else coming up unless terrorists begin to surface and attack us, and I think they've been disrupted."

The buoys are a sign of the second barrier installed in front of Bagnell Dam. The first was built about 15 years ago to prevent boaters from getting too close if plant operators ever use the plant's flood gates.

Lou Mayer, the vice president of a boating safety association at the lake, said the security buoys won't interfere with anything else at the lake.

"This keeps subversive activity away from the area," he said. "If anyone has a quarrel with that, shame on them."