DNR wants bubbling barrier against carp in St. Croix

DNA in river accelerates plan to block leaping invaders at Prescott.

In response to new evidence that Asian carp may be swimming in Minnesota waters, the state's natural resource officials are accelerating a plan to build a multimillion-dollar sonic bubbler across the mouth of the St. Croix River at Prescott, Wis.

"This is a high priority for the governor, and we don't have another project in the pipeline," said Tom Landwehr, commissioner of the Minnesota Department of Natural Resources. "But we feel it's imperative that we do something."

Next week, DNR officials will present the idea to the Lessard-Sams Outdoor Heritage Council, the group that recommends how to spend much of the 2008 Legacy Act sales tax money. The barrier, which would deter carp but not other species, would cost a minimum of $7 million to build. It would be the first time such a system had been used across a major river, and it's not guaranteed to work.

Landwehr said, however, that it's the only viable option now and that Legacy funds are the only source of money.

Last week, the DNR announced that it had found DNA evidence that at least one type of Asian carp could be in the St. Croix. It found DNA from the notorious leaping silver carp at 22 of 50 sites it tested, but none from any of the other three species of carp believed to be moving upriver from Illinois and Iowa.

This week, state fishery officials were looking hard for the real thing with nets in the St. Croix and Mississippi rivers, but as of late Thursday, they hadn't caught any. Later this month, the DNR will contract with commercial fishing operations to do the same thing on a much larger scale.

But the strong DNA evidence has pushed the state to act. "We never had urgency before today," Landwehr said.

He said the DNR is likely to ask the Lessard-Sams council to recommend that the Legislature approve funding for a barrier even if detailed plans are still uncertain.

Bill Becker, executive director of the Lessard council, said it is the first time in the council's three-year history that it will consider funding a project after its July 15 deadline.

"It seems to me they suddenly have a sense of urgency that they didn't have six weeks ago," he said. "There are all kinds of questions that need to be asked and answered."

The greatest among them is how well it would work.

Sound and bubble barriers have worked in smaller rivers, but they haven't been tried on the scale that would be required for the St. Croix. The barriers combine a curtain of bubbles with sound pitched at a level that the noise-sensitive fish don't like.

"They discourage fish but don't block them," said Steve Hirsch, the DNR's director of ecological and water resources. "They are used most successfully where fish have a choice."

In short, they could choose to bypass the St. Croix and continue up the Mississippi, he said. The next barrier would be the Coon Rapids dam. The Legislature authorized $16 million in bonding to refurbish the dam as a barrier. But many experts say that, too, is likely to be a temporary fix.

Even if both projects were completed, it would leave much of the state vulnerable to the fish, including Lake Pepin and the Minnesota River basin. The only way to protect them would be to close one of the lock and dams in southern Minnesota, and Hirsch said that since the fish are already in Iowa, it may be too late for that.

"You don't want to lock the barn door after the horse is out," he said.

The only certain protection for the northern part of the state would be closing one of the lock and dams in the metropolitan area at a point that is too high for the fish to breach or swim around during floods.

That would be the Ford Dam or, better yet, the lock and dam at St. Anthony Falls in downtown Minneapolis. At one time, that was a significantly high natural barrier in the river.

But, Hirsch said, that would be up the Army Corps of Engineers, and officials from that agency have repeatedly said closing any of them would require an act of Congress.

Josephine Marcotty • 612-673-7394

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