A new study confirms that lakers - the freighters that move iron ore, coal and other bulk material between the Great Lakes - carry invasive species that originated in countries thousands of miles away.

The study, supported by the maritime industry and conducted by the Superior-based Great Waters Research Collaborative, found six species of foreign zooplankton when researchers checked the ballast of 10 different lakers from both the U.S. and Canadian companies, none of which ever see the ocean.

It's likely the invaders first came to North American ports in saltwater ships but were being moved between the lakes by the lakers.

Five of the foreign species, including one called the bloody red shrimp, have not yet established in western Lake Superior. The sixth species, Paraleptastacus wilsoni, had never been found in any of the Great Lakes before.

Some of the species live in harbor sediment and may have escaped usual efforts to find new species, the study's authors noted.

The study did not look into whether the foreign species found in the laker ballast water are likely to establish viable populations in the region or what impact they will have if they do.

Sampling took place in 2017, primarily in the late summer through early winter, and focused on ballast water discharges in Duluth and Superior of water loaded from ports in the lower four Great Lakes.

Allegra Cangelosi, lead investigator of the study, said ship owners in the U.S. and Canada cooperated with the researchers.

"Their willingness to support this research demonstrates their strong commitment to the health of the Great Lakes," she said, adding that it remains unknown if the new species might become a problem here. "The results nonetheless support greater research emphasis on identifying and validating performance of new ballast water management alternatives for lakers."

Federal ballast water regulations that are set to require onboard water treatment in saltwater ships in coming years don't apply to ships that never leave the Great Lakes. But Minnesota has rules on the books that will require lakers to treat ballast just like salties.

While the foreign species may have come across the ocean in saltwater vessels, regulators say lakers move millions of gallons of ballast water between infested ports every year and are a likely pathway to spread invaders, especially in and out of Duluth-Superior, by far the busiest of Great Lakes ports.

Minnesota now has rules on the books to apply the International Maritime Organization standards to lakers after each boat's first dry-dock starting in 2019, with all completed by about 2023, unless boat owners can convince regulators that it's not possible. (Wisconsin had a similar rule but dropped it recently.)

The U.S. Environmental Protection Agency paid for the study via the U.S. Maritime Administration as part of the Great Lakes Restoration Initiative.

Bruce Burrows, president of the Chamber of Marine Commerce, noted that Canadian shipowners have invested $1.5 million trying to find a ballast water treatment that will fit on Great Lakes freighters "that are both operationally and economically feasible for the Canadian domestic fleets'' and that they remain committed to finding a solution.

John Linc Stine, commissioner of the Minnesota Pollution Control Agency, said the study is "an important benchmark in protecting Lake Superior and inland waters from unwanted, aquatic species."

"Now it's time to get to work with the vessel owners to develop additional ballast management strategies that further protect Minnesota waters,'' Stine said in a statement.