Fortifying an Illinois waterway to prevent invasive carp from using it as a path to Lake Michigan could cost nearly three times as much as federal planners previously thought, according to an updated report.

The U.S. Army Corps of Engineers this week released a final strategy plan for upgrading the Brandon Road Lock and Dam near Joliet, Ill., which experts consider a good location to block upstream movement of Asian carp that have infested the Mississippi and Illinois rivers.

Scientists warn that if the voracious carp become established in the Great Lakes, they could out-compete native species and harm the region's $7-billion fishing industry.

The new plan by the corps is similar to a draft from August 2017, but the estimated price tag has jumped from $275 million to nearly $778 million.

"Basically during the past year, some additional engineering and design work changed the scope to bring it up to that current cost," Allen Marshall, spokesperson for the district office of the corps in Rock Island, Ill., said Wednesday.

The biggest increase is for building an "engineered channel" at Brandon Road. The lock-and-dam complex is on the Des Plaines River, which forms part of the waterway link between Lake Michigan and the Illinois River, a tributary of the Mississippi.

Asian carp first started showing up in North America in the 1970s, when they were brought in for the aquaculture industry in the U.S. and for the live food fish industry in Canada. (Illinois Department of Natural Resources)

Under the plan, the channel would contain devices, including an electric barrier, noisemakers and an air bubble curtain to deter fish from swimming upstream and remove those that don't turn back. The adjacent lock would be retooled to flush away unwanted species floating on the water.

The draft had proposed using water jets to dislodge fish that might be stunned or caught in gaps between barges. But the new version says a better method would be generating a continuous, dense curtain of air bubbles in the channel.

Even though the price tag for the proposal has jumped, the Great Lakes Fishery Commission wants the project to move forward.

"Without it, it would be a relatively straight shot into Lake Michigan. So yeah, let's get on with it," said Marc Gaden, communications director.

"It's a $7 billion dollar fishery, let's keep that in mind."

He said once the Asian carp get into the Great Lakes, they become a "permanent, destructive" addition to the ecosystem.

The army corps is accepting public comments through Dec. 24 and expects to submit the plan to Congress in February. Its timetable envisions congressional authorization and initial funding next year and the signing of building contracts by July 2020, with work completed by March 2027.

Several states that border the lakes, including Michigan and Illinois, agreed previously to discuss sharing the costs. The escalating price could complicate those negotiations.

Asian carp prefer cool water temperatures like those found near the shores of the Great Lakes. (CBC)

"Now that the cost has nearly tripled to $778 million, we need to have a better understanding of how this project, with all the proposed components, actually reduces the risk of Asian carp and other invasive species getting into our Great Lakes in a fiscally responsible manner," said Ed Cross, spokesperson for the Illinois Department of Natural Resources.

Tammy Newcomb, water policy adviser for the Michigan DNR, acknowledged feeling "sticker shock," but said it shouldn't derail the project.

"Given the costs of Asian carp invading our Great Lakes, inaction is not an option," said Sen. Debbie Stabenow, a Michigan Democrat and co-chair of the Senate Great Lakes Task Force.

Carp have infested much of the Mississippi River basin and are threatening to gain a foothold in the Great Lakes through rivers and canals. (Kelly Bennett/CBC)

Illinois officials and business groups have questioned the need to drastically re-engineer the lock and dam, particularly if it would slow barge traffic on the busy commercial waterway.

Lynn Muench, a senior vice-president of the American Waterways Operators, which represents barge companies, said the army corps report sidesteps whether Asian carp are likely to reach Lake Michigan in sufficient numbers to thrive. It also has no cost-benefit analysis of the proposed deterrents, she said.

Meanwhile, environmentalists were concerned that the army corps budget for next year includes no money for pre-construction engineering and design work to get things moving.

"How serious is the Trump administration about getting this project constructed if they haven't put the necessary funding in to keep it moving on schedule?" said Molly Flanagan, a vice-president of the Alliance for the Great Lakes.