Agencies concerned about the Great Lakes have recommended that a massive barrier be built to protect the lakes from an aggressive species of fish.

The Asian carp's voracious eating and breeding habits have environmentalists worried that the fish will overrun the Great Lakes and damage the ecologically fragile area.

In a bid to prevent a school of scaled invaders from entering, two organizations issued a report Tuesday calling for a large physical barrier to be placed between the lakes and the Mississippi River watersheds.

Tim Eder, executive director of the Great Lakes Commission, has called a barrier the "best long-term solution for preventing the movement of Asian carp and other aquatic invasive species."

The Commission, along with the Great Lakes and St. Lawrence Cities Initiative, has suggested three possible ways to close the gap between the lakes and the river.

• A single down-river barrier between the two drainage basins

• Barriers in five locations near Lake Michigan

• A "mid-system" option that would come close to restoring a natural divide between the watersheds, broken more than a century ago

The report doesn't recommend a particular option but says the mid-system method is the least costly of the three multi-million dollar solutions.

There is already an electric barrier in place about 60 kilometres away from Lake Michigan, said David Ullrich of the Great Lakes and St. Lawrence Cities Initiative.

"Although that appears to be slowing down the fish, there is evidence that some may have gotten beyond the barrier," he told CTV's Canada AM on Tuesday.

Aquatic vegetation and creatures such as zebra mussels are also not deterred by the electric barrier, he added.

That's why Ullrich says additional measures are necessary, and soon.

The U.S. Army Corps of Engineers has said that as many as 10 invasive species are poised to enter the Great Lakes from the Mississippi River.

Economic projections place the costs of the barriers between $100 and $150 million.

However, Ullrich said the total cost of the infrastructure project could range anywhere between $3 and $9 billion over a 50-year period. That includes flood control, water quality tests, transportation issues and more.

The Corps of Engineers are conducting their own study of how to close the divide between the two waterways but those findings aren't slated for release until late 2015.

"While we recognize and support the work being done by others to find solutions to the Asian carp threat, we need to appreciate fully the urgency of this matter," Ullrich said in a news release.

Preventing just one invasive species from entering the Great Lakes could save as much as $5 billion over 30 years, according to the report.