A tiny New Zealand snail is threatening a multi-billion dollar sport fishing economy after it was found in the Great Lakes of North America.

The tiny New Zealand mudsnail, which can boom to phenomenal densities, has been found thriving in Michigan for the first time.

It was spotted by an aquatic biologist on a floating trip down the Pere Marquette River in August, reported the Detroit Free Press.

"I thought, 'There are a lot of really small snails here. I wonder what they are? I haven't seen anything like this before'," said Sarah LeSage who works for the Aquatic Invasive Species Program Coordinator with the Michigan Department of Environmental Quality.

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Samples confirmed they were the New Zealand mudsnail - an invasive freshwater species that can reproduce asexually and at staggering levels.

The highest concentration of New Zealand mudsnails ever reported was in Switzerland's Lake Zurich where the species colonised the entire lake within seven years to a density of 800,000 per square metre.

While it is widespread in the western states of the United States, it now appears to have made its way into Michigan's lakes.

Seth Herbst, the Aquatic Invasive Species Coordinator for the state Department of Natural Resources, told the Detroit Free Press it was likely they had travelled there on the boots or waders of fishermen.

There are fears that they could majorly affect the state's US$2 billion a year sports fishing economy.

"A single female can result in a colony of 40 million snails in one year," Mr Herbst told the paper.

"When they get to be that dense, they out-compete some of the native species."

Surveys since the August discovery have shown the mudsnail is "a little more widespread" than was initially hoped.

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There is no effective treatment to kill the snails, the paper said.

But boaters and fishermen are urged to help prevent its spread by thoroughly rinsing and drying their boats, trailers, boots, waders and other gear after trips on the waterways.

"People's awareness in general can help us make these early detections - and that can make a difference in early response actions to prevent the spread of invasive species," Ms LeSage said.

"You don't have to be a technical person to say, 'Something looks out of the ordinary here'."