CHICAGO —  Connections engineered more than a century ago between the Great Lakes and the Mississippi River watershed should be changed to block the advance of invasive species that can cause irreversible damage, an environmental advocacy group says.

Separating the two basins is the only way to stop the transfer of some species, including the voracious Asian carp that is within 50 miles of Lake Michigan, says a feasibility study issued Wednesday by the Alliance for the Great Lakes.

"If you want to protect the Great Lakes, this is what you have to do. Invaders like Asian carp are unpredictable, but their effects are catastrophic and irreversible," said Joel Brammeier, Alliance vice president and lead author of the study. "You've got to remove their pathway."

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Researchers fear the carp, which can grow up to 100 pounds and more than 4 feet long, could eat all the food that's available for other species in the Great Lakes ecosystem, possibly leading to the collapse of the lakes' multibillion-dollar fishing industry, Brammeier said.

Scientists say more than 150 invasive species have entered the Great Lakes, multiplying rapidly and feeding on native species or outcompeting with them for food.

Millions of dollars have been spent trying to control the zebra mussel and round goby, which already have moved between the Great Lakes and Mississippi River basins.

Millions also have been spent on electrical barriers across the Chicago Sanitary and Ship Canal south of the city to keep Asian carp out of Lake Michigan.

The Alliance says the barriers, which deliver a non-lethal jolt to fish, have been effective, but are not a long-term solution.

There are no natural connections between the Great Lakes and Mississippi River watersheds.

More a century ago, engineers linked them with a complex network of manmade canals and existing rivers to reverse the flow of the Chicago River and keep waste from flowing down it to Lake Michigan, which Chicago uses for drinking water.

Possible changes include erecting concrete walls and constructing more shipping locks, according to the study. It does not make explicit recommendations, but calls on the U.S. Army Corps of Engineers and Environmental Protection Agency to conduct further study.

"The EPA is very concerned about the impact of invasive species on the health of the Great Lakes. Limiting their spread is important for protecting the Lakes and we need to look at all options for controlling their movement," EPA spokeswoman Phillippa Cannon said. "We welcome suggestions from the Alliance and look forward to reading its report."

Corps spokeswoman Lynne Whelan in Chicago would not comment specifically on the Alliance study. She said the Water Resources Development Act of 2007 authorizes a Corps study that includes looking at ecological separation of the watersheds, but no funding has been authorized.

The alliance's study — funded by the Great Lakes Fishery Commission and Great Lakes Fishery Trust — gives general cost ranges for some projects. The cost of the most complicated, such as installing a sterile lift to transfer barges between the two watersheds, is listed only as "expensive."

Although locks could enable shipping to pass while blocking invasive species, any type of barrier would slow traffic and cost money, said Stuart Theis, executive director of the United States Great Lakes Shipping Association. Still, he would cautiously support efforts to separate the watersheds.

"We wouldn't object to efforts that would keep invasive species out of the Great Lakes," he said.