PIERRE, S.D. - Bright, flashing strobe lights like those that musicians use on stage have been shown to repel smelt, a tiny bait fish whose main job is to serve as lunch for walleyes.

But it might not be practical to use the lights to prevent smelt from being flushed through the water intakes at Oahe Dam, said Dennis Unkenholz, fisheries chief for the state Game, Fish and Parks Department.

"While, in theory, the study showed you could do it and have an expectation of having some impact, all the practical issues haven't been worked out," he said.

When water levels are high in Lake Oahe, one of six Missouri River dams, smelt can be sucked into the intakes and flushed through concrete tunnels that carry water a half mile under the dam to power plant turbines. That happened in 1997 and 1999, and officials estimated that more than 400 million smelt went through the intakes and downstream into Lake Sharpe in 1997.

The problem has dissipated in recent years, courtesy of the drought, said Jack Erickson, a GF&P fisheries biologist. With the water level lower, smelt are swimming well below the intakes, he said.

It would not be worth spending money to install the flashing lights if smelt are rarely in danger of being sucked into the intakes, Erickson said.

The smelt population had taken a nosedive, partly because so many were flushed through the intakes, and Lake Oahe was left with stunted, skinny walleyes. In recent years, the balance between predator and prey has been restored, and Oahe's walleye population has rebounded along with smelt numbers.

But the smelt recovery was hampered by the drought, which started about a half dozen years ago.

Smelt are a slender, silvery fish that grow to 5 inches to 8 inches long. They spawn in the spring in less than a foot of water near shore. Water levels that fell during April and May in some years left eggs high and dry.

Smelt are spawning now on Lake Oahe, and conditions look good for successful reproduction, Erickson said. "We are seeing an improvement in the smelt population since 2001."

After so many smelt were lost through the intakes in 1997 and 1999, research was conducted in 2004 and 2005 by two South Dakota State University graduate students, Nathan Richards and Marty Hamel, along with Steven Chipps and Michael Brown of the university's Fisheries and Wildlife Research Unit.

Research indicated sound had little effect but that lights pushed back the smelt.

"Yes, light can move these fish a significant distance and repel them," Erickson said.

But attaching strobe lights to the intakes might not be practical, Erickson said. The lights cost $10,000 each, and many would be required to cover the entire intake structure, the biologist said.

And the lights likely would not be worth the cost if they were needed only every 30 years or so, Erickson said.

Smelt swim beneath the thermocline, which is the boundary between cold water below and warmer water above, Erickson said.