Asian carp, an invasive aquatic species threatening the Great Lakes. Photograph: Manuel Balce Ceneta/AP.

The fight looks utterly unequal. In the red corner: the combined might of North America, including the US and Canadian governments, the US army, the governors of eight American states, two Senate c­ommittees and the supreme court. In the blue corner: one fish.

The way things are looking, the fish is winning.

At stake is the health of the Great Lakes, the world’s largest body of fresh water. Environmentalists warn of ecological disaster, courtesy of Asian carp, an invasive species of food-guzzling fish that is within miles of entering Lake Michigan.

If they do, they would have the ­potential to spread throughout the lakes, wreaking havoc to their ecosystem and with it the $7bn (£4.7bn) fishing and recreation industries on which millions of jobs depend. “This is an intense threat, and people are just waking up to how big the danger is,” said David Ullrich of the Great Lakes and St Lawrence Cities Initiative, which represents 70 waterfront cities in the US and Canada with a joint population of 13 million.

Asian carp were first introduced to southern states of the US from China in the 1970s to help clean tanks in fish farms. They escaped and for more than 30 years have steadily worked their way up the Mississippi river system, devouring food and devastating native fish populations along the way. Last December, DNA of the carp was found just a few miles from the Great Lakes outside Chicago, a discovery that Ullrich described as “a major shock to everyone”.

Though they live on plankton and algae, Asian carp are like the Terminators of the fish world. They can grow to four feet and 110 pounds, and eat up to 40% of their body weight in a single day. By sucking up so much goodness from the water they deprive the juveniles of native species of their primary source of food, leading to their decline.

Further downstream from the Great Lakes, in the Illinois and Mississippi ­rivers, the damage is already abundantly evident. The newcomers have starved out native species to such an extent that Asian carp now account for more than nine out of every 10 fish.

The fear is that if they become established in the Great Lakes the same brutal transformation will occur.

The lakes are considered all the more susceptible because they were formed at the end of the last ice age as the glaciers receded. That was 10,000 years ago, which in biological terms is a blink of an eye, rendering this young ecosystem all the more vulnerable to invasive attack.

As an additional threat, the silver variety of Asian carp also have the ability to leap two metres into the air, which they do when disturbed by ­vibrations of passing motor boats. Such acrobatics would be quaint were they not so perilous.

“These fish have broken jaws, knocked people unconscious and caused folks to nearly drown in the Mississippi river,” said Joel Brammeier of the environmental group Alliance for the Great Lakes. “Imagine cruising down a lake at 20 knots and getting hit in the stomach or head with a bowling ball – that’s what you can envisage with Asian carp.”

With the fish now within striking distance of the lakes, an extraordinary array of officialdom has begun to engage with the problem, from small fishing and shipping firms right up to the federal government, Congress and supreme court. Everyone is agreed that the fish must be stopped, but consensus on how to do so is proving elusive.

Earlier this month the Obama administration put forward a $78.5m plan for blocking the fish. Its focus lies in an electronic barrier that has been built by the US army corps of engineers across a canal through which the fish would have to swim to reach the lakes. The barrier, opened last year, has been designed to allow ships to pass while deterring fish. It works by shooting a high-voltage current through the water strong enough to stun, but not kill, the carp.

The crucial question is whether it is foolproof. “I don’t think we can ever guarantee 100% of anything in life, but we think it’s well above 99% of the fish that are turned back,” said Chuck Shea, who manages the barrier.

But for those who fear that arrival of the fish would spell disaster, that 1% risk is simply too high – particularly as the carp DNA found last December was beyond the barrier. The state of Michigan, supported by Minnesota, Wisconsin, Ohio, Pennsylvania and New York, all of which have Great Lakes shores, has taken the matter to the supreme court to force through a permanent solution.

These states are pressing for the ultimate barrier: they want to set the clock back 110 years to when the lakes were distinct from the Mississippi river system. It was only in 1900 that the connection between the two was made when, in a breathtaking – some say breathtakingly arrogant – feat of engineering, the flow of the Chicago river was reversed to allow billions of gallons of waste water to be sent downriver from Chicago thus solving the city’s sewerage problem.

As a result of the reversal, Lake Michigan was artificially joined by canal to the Illinois river and hence the Mississippi, providing the Asian carp more than a century later with an artificial pathway into the Great Lakes.

Michigan wants that pathway to be cut off, by sealing the locks that link the two ecosystems. The state, whose economy is singularly dependant on the Great Lakes by dint of its long shoreline, is not satisfied by the Obama administration’s proposal merely to restrict use of the locks. Michigan’s attorney general recently denounced the federal plans as “half-measures and gimmicks”.

Against that view, the state of ­Illinois has been pressing for the locks to remain at least partially open. Economic ­imperative is at work here, too.

Chicago, a city whose greatness was ­initially founded upon shipping, still has a small but significant trade in heavy materials such as coal and gravel by barge along the canal through which the carp are now progressing in the opposite direction.

Judy Biggert, a Chicago member of congress, has labelled the outcry over Asian carp “hysteria” and ridiculed Michigan and others for their “act now, think later mentality”.

The fear for environmentalists is that while this largely economically-driven squabbling goes on, Asian carp will be allowed to continue gobbling their way towards Lake Michigan. Should they be allowed to reach there in numbers ­sufficient to start a breeding colony — and females can spawn more than a ­million eggs several times in a season — it will all be over bar the shouting.

Brammeier sees Asian carp as a crucible for the lakes, pointing out that they have already been severely harmed by toxic waste and 180 previous invasive species. “We know so much about this new threat. If, after all that, we still can’t act, if we stand down, then we will be confining the Great Lakes to another century of damage and degradation.”