The Great Lakes, which contain about a fifth of the world’s fresh water, were landlocked until the Erie Canal opened in 1825, allowing in predators like the sea lamprey that sucks the blood from native lake trout.

More than 180 other invasive species made their way to the Great Lakes through canals and the St. Lawrence Seaway including alewives, which eat lake trout eggs and baby trout, and zebra mussels, which clog pipes and help spread bird-killing botulism. Invasive species cost the Great Lakes region more than $100 million a year. Trillions of quagga mussels carpet much of the bottom of Lake Michigan. Like zebra mussels, quagga mussels eat plankton, taking food from native fish, and populations of salmon, whitefish and native mussels have plummeted.

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The problem is poised to get worse. Much worse. Silver and bighead carp, two types of Asian carp, are making their way up the Illinois River toward Lake Michigan. Asian carp can grow up to 4 feet long and 100 pounds and eat the food native fish depend on.

They could make up as much as a third of the weight of Lake Erie’s fish if they establish themselves in the Great Lakes. The fish could also spread to rivers and streams in Wisconsin, Michigan, Indiana and Canada from the Great Lakes.

In June, an 8-pound, 28-inch adult silver carp apparently somehow got past electric barriers in the Chicago Sanitary and Ship Canal and was caught by a commercial fisherman just nine miles from Lake Michigan. No other silver carp have been found past the barriers, but another type of Asian carp, grass carp, are in Lake Erie, Lake Michigan and Lake Ontario.

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“Asian carp are like cockroaches,” said Henry Henderson of the Natural Resources Defense Council. “When you see one, you know it’s accompanied by many more you don’t see.”

A study for the U.S. Army Corps of Engineers, scheduled to be released Aug. 7, is expected to focus on trying to stop the advance of the fish at the Brandon Road Lock and Dam near Joliet, Ill.

A draft of the study, which was expected to cost $8.2 million, was originally supposed to be released Feb. 28, as I earlier wrote in DCReport.org, the journalism nonprofit founded by Pulitzer Prize winner David Cay Johnston. Sixteen Republican U.S. House members, mostly from Illinois and Indiana, asked Trump to sit on the report until after the Senate confirms a new Army assistant secretary to oversee the Corps of Engineers. No one has been nominated for that position.

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The representatives wrote that owners of commercial vessels and their employees are concerned that the report would recommend structural changes to the Brandon Road Lock and Dam that would “disrupt commercial activity . . . and harm the local, regional and ultimately the national economy.”

The report could recommend building a channel with an electric barrier, flushing lock system and noise cannons with a price tag of up to $270 million.

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The report was scheduled for release only after the U.S. Senate Appropriations Committee approved a bill to force its release.

Michigan lawmakers, including U.S. Rep. Fred Upton, a Republican, and U.S. Rep. Debbie Dingell, a Democrat, wrote Trump that releasing the report “is an essential next step to ensure we safeguard our region’s $7 billion fishing industry, $16 billion boating industry, and $18 billion hunting and wildlife observation industry.”

More than a century ago, Chicago rerouted its sewage through the Chicago Sanitary and Ship Canal so the city wouldn’t dump it into Lake Michigan, opening a conduit between the Great Lakes and the Mississippi River basin. The canal acts like a superhighway for invasive species.

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Five states – Michigan, Wisconsin, Minnesota, Ohio and Pennsylvania – unsuccessfully sued the U.S. Army Corps of Engineers to try to get the Corps to close off that conduit to the Mississippi River basin.

Asian carp were brought to the United States to control algae in catfish ponds and waste-treatment plants in Arkansas and Mississippi. They escaped into rivers after flooding or were released and made their way up the Mississippi River.

Havana, Ill., on the Illinois River, about 200 miles from Lake Michigan, has been called ground zero for silver carp and bighead which jump out of the water when startled. Boaters have suffered broken noses and jaws.

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“It’s literally raining fish,” Kevin Irons, of the Illinois Department of Natural Resources, said in 2014. “It is raining carp.”

Biologists talk about invasive species by using a measurement called an invasion curve. Eradication becomes less likely the more established an invasive species gets.

Nicholas Mandrak, an associate professor at the University of Toronto, said there is only a small window for action.

“Within a year of their hatching, they become too large for any predator to eat,” Mandrak said.

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Grass carp lay between 500,000 and 3 million eggs at a time and might spawn twice a year. They are the only species of Asian carp with teeth and eat 20 percent to 100 percent of their body weight a day in plant matter.

Female silver carp also produce about 500,000 eggs. Female bighead carp carry 660,000 to 872,000 eggs. Bighead carp don’t have a true stomach and constantly eat.

Since 2010, commercial fishermen, who are paid to catch Asian carp as part of the effort to deter their spread, have pulled more than 5.5 million pounds of silver carp and bighead carp from the Illinois River upstream of Starved Rock State Park near Oglesby, Ill.

A fourth type of Asian carp, black carp, which eats mussels and snails, was caught in April in the Illinois River south of Peoria. A mature female black carp can produce 129,000 to 1.18 million eggs a year.

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“We’ve got four species doing damage to different parts of the ecosystem,” said biologist Dan Stephenson, the chief of fisheries for the Illinois Department of Natural Resources.

In Lake Erie, the shallowest of the five Great Lakes, the annual summer algae bloom is spreading, making parts of the lake look like someone spilled pea soup into it. In 2014, bacteria from the bloom forced the water system in Toledo, Ohio to be shut down for three days.

The Great Lakes algae, fed by runoff from farms and by sewage treatment plants, would also be a food source for Asian carp. Grass carp also contribute to algae blooms because they digest about half the plants they eat and excrete the rest.

Scientists are researching ways to try to slow the spread of Asian carp such as a microparticle embedded with a poison that kills Asian carp but not native fish and fences made of carbon dioxide which repel the fish. They hope the Great Lakes fisheries won’t be overrun by Asian carp like the Illinois River.

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“There are more Asian carp in Illinois than in China,” Stephenson said.