Lee Bergquist

Milwaukee Journal Sentinel

A plan to improve fish populations by letting them swim through a Wisconsin River dam has languished for years as officials wrestle with the possibility that Asian carp could also unwittingly slip through.

The dam at Prairie du Sac, about 30 miles northwest of Madison, has produced electric power since 1914. But more recently, it has also served as a barrier against invading bighead carp — a non-native fish that’s wreaked havoc in other waters.

RELATED:In latest discovery, DNR finds four bighead carp in the Wisconsin River near Prairie du Sac

In November 2017, state Department of Natural Resources crews captured four bighead carp just below the dam while conducting routine surveys. They found a fifth on the shoreline that was dead.

There have been other, isolated finds of bighead carp in Wisconsin, on the Wisconsin-Minnesota border, dating back to 1996, primarily along the Mississippi River, according to the DNR.

But the discoveries at Prairie du Sac are the farthest inland in Wisconsin, threatening an estimated 100 miles of the Wisconsin and Baraboo rivers if bigheads got through the dam, according to state and federal officials.

Bigheads feast on plankton, and their prolific appetites have wiped out food sources for native species in other waters, putting the fish and other Asian carp front and center in policy debates about how to deal with invasive species.

RELATED:A Watershed Moment

To the south, bighead and another Asian species, silver carp, are firmly entrenched in the Illinois River. Today, the last line of defense from the fish entering Lake Michigan is an electric barrier system on the Chicago Sanitary and Ship Canal.

Keeping carp at bay

The threat of Asian carp invading Lake Michigan has garnered most of the public’s attention. That’s especially so with silver carp, which are known for leaping out of the water.

But both species have been found in the upper Mississippi system, with the Minnesota Department of Natural Resources reporting in late spring the capture of several bigheads on the St. Croix River on the Wisconsin border.

With the Prairie du Sac dam currently blocking upstream movement of bigheads, there appears to be little urgency in Wisconsin to require the dam’s owner, Alliant Energy of Madison, to move ahead with a fish passage system for now.

“There is no reason to rush things now,” said biologist Nick Utrup of the U.S. Fish and Wildlife Service. “The dam’s been there for a 100 years. We want to do it right.”

DNR biologists say there is no evidence bighead carp are reproducing in the Wisconsin River. This might be attributable to better water quality — less algae — for the fish to feed on compared with many other Midwest rivers in the Mississippi basin.

RELATED:Videos show fish swimming through barrier meant to stop Asian carp

When Alliant’s license to generate electricity on the river was re-approved by federal authorities in 2002, the company was required to install fish passage.

According to the DNR, there are 10 such systems among Wisconsin's fleet of 3,900 dams.

Alliant pushed for a go-slow approach and a spokesman said it has made its sentiments known in political circles.

The Fish and Wildlife Service agreed to push back the deadline for fish passage from Dec. 31, 2020, to 2025, in part, because the agency must finish an environmental assessment of the impacts. Work on the assessment stopped a few years ago, Utrup said, as public concern over Asian carp grew.

Last week, two Wisconsin congressman — Reps. Glenn Grothman, a Republican from Sheboygan County, and Mark Pocan, a Dane County Democrat — introduced a bill requiring the Fish and Wildlife Service to consider the threats posed by invasive species before requiring that fish passage be built.

They took similar action last year by adding an amendment to a hydropower re-licensing bill that passed the House. The amendment did not pass in the Senate.

In that 2017 debate, Grothman said his chief concern was Alliant’s Prairie du Sac dam.

“Below that dam, we had Asian carp, an invasive species, a huge fish,” he said, according to a House transcript.

“If that fish was able to get further north on the Wisconsin River, because of a fishway, you could wind up with this invasive species not only in the northern part of the river, but, and quite frankly, in dozens of lakes throughout northern Wisconsin.”

In fact, another Alliant dam located in Wisconsin Dells serves as the next barrier to the north.

Company spokesman Scott Reigstad said in an email that the utility began raising concerns in 2012 that construction of a fish passage system, which is estimated to cost $15 million to $20 million, “could allow invasive species like Asian carp to pass through the dam and migrate to Lake Wisconsin and the upper Wisconsin River.”

Reigstad said when the company was first required to build fish passage, “Asian carp species had not yet been detected in the waters below the Prairie du Sac dam. Now they have on multiple occasions.”

A separate, $55 million upgrade to the aging dam now underway is not part of the fish passage debate, he said.

Passage precautions studied

John Lyons, a fisheries scientist now retired from the DNR, said he and others at the agency spent considerable time planning to move fish through the dam.

The plan, as envisioned, would have employed an elevator-like apparatus used at key periods such as spawning season to bring fish into a holding area where they would be examined and sorted.

The main objective: Allow lake sturgeon, blue sucker and paddlefish, a highly distinctive species with a spoon-shaped snout, to make unimpeded, long-distance upstream and downstream spawning migrations as a way to increase populations and improve genetic diversity.

“The issue of invasive species, particularly invasive Asian carp, was always a big issue,” said Lyons, now curator of fishes at the University of Wisconsin-Madison’s zoological museum.

“Much of the time we spent was to make sure there was no accidental mishaps,” he said, noting that every fish released upstream would be done so with multiple checks from trained biologists.

Then, about four or five years ago, the work stopped.

Lyons said top officials made it clear that staff should devote their time to other projects. “There wasn’t a lot of explanation,” Lyons said.

Mark Aquino, a DNR administrator who was involved in the project, said the agency supports the notion of moving fish over the dam. But he said that the logistics of doing so needs more study.

He said that the next step should be the Fish and Wildlife Service’s environmental assessment — a project now on hold.

“We have to make sure the potential risks are thoroughly evaluated,” Aquino said.

Want more stories like this? Subscribe to the Journal Sentinel today.