PORTLAND – Maine officials are already well aware of the threat posed by milfoil to ponds and lakes. But the prospect of the aquatic invader being spread by boats is much greater than previously believed.

A report that will be presented to the Legislature next week indicates more than 1,200 boats inadvertently carry plants around Maine each summer, offering ample opportunity for aquatic milfoil to infest and choke lakes.

Peter Lowell of the Lakes Environmental Association in Bridgton said that, given the report’s findings, it’s a wonder Maine isn’t already under siege by the plant.

“The bad news is that we know we’re vulnerable,” Lowell said. “I think the question we’re all asking ourselves is why aren’t we worse off. We’re feeling very lucky, but that’s no reason to be complacent.”

Milfoil is an invasive plant that can be spread from lake to lake on a trailer or boat propeller. Once introduced, the plant spreads quickly and forms dense mats of vegetation that harm native plants, destroy fish habitat, and interfere with swimming and boating.

Lawmakers have created an invasive-aquatic species program, launching widespread educational programs, voluntary boat inspections and a new requirement that freshwater boaters purchase stickers to pay for it all.

Beginning this year, Maine residents will pay $10 for green-and-blue stickers that must be displayed on their boats. Out-of-staters will pay $20. The sticker program eventually is expected to bring in as much as $1 million a year.

But the report by the Maine Department of Environmental Protection and the Maine Department of Inland Fisheries and Wildlife concludes that more needs to be done to educate boaters and help them change their behavior.

It also recommends that voluntary inspections of boats and trailers continue at launch ramps this summer to catch plants before they hit the water.

Ten sites already have been infested with variable milfoil, including Sebago Lake, Pleasant Pond in Gardiner and Richmond, Cushman Pond in Lovell and Lake Auburn.

Eurasian milfoil, a more aggressive plant, was carried into Crystal Lake in Gray by plant fragments on a boat. It will be a year or two before biologists can determine whether the plant has established itself.

Lowell said the Lakes Environmental Association would be looking for ways that local municipalities can augment the state program, especially through the use of more volunteers

“We see the state program as a huge benefit, but there aren’t enough dollars in state government to solve this problem,” he said. “We need to all participate in it.”