Minnesota is ratcheting up the penalty for boaters who are caught with zebra mussels in their dry wells or milfoil hanging from their trailers: mandatory education. On top of fines of $100 to $500, this spring boat owners caught violating boat cleaning rules designed to stop the spread of aquatic invasive species will also have to take 20-minute online class and a quiz.

And they can't use their boat again until they pass.

It's an unusual strategy, said officials from the Minnesota Department of Natural Resources (DNR). Many states have online courses available, but they said didn't know of any others that require it of violators.

"We hope this will increase our rate of people who understand what's going on," said Heidi Wolf, supervisor of the DNR's invasive species unit. "Even though it's just a few individuals, they are at high risk for infesting a water or a river."

Awareness among Minnesota boat owners is high and growing, said Keith Bertram, DNR enforcement officer. When the agency first started random roadside boat inspections, only half the owners were in compliance, he said. Now, it's more like 86 percent, he said.

The DNR is relying on fines, education and boat inspections in an effort to reduce the spread of milfoil, zebra mussels, spiny water flea and other invasive species. Today, about 5 percent of the state's 11,000 lakes and rivers are infested with one or more of them.

State law requires boat owners to rinse and drain all cavities and dry wells in boats, keep them unplugged between uses and to remove all vegetation from boats and trailers after pulling them out of any lake or river. Dock owners must let their docks dry for 21 days before moving them one place to another. Bait buckets should be emptied in the trash, not a lake.

There are other rules for commercial operators who use a variety of equipment.

Meanwhile, University of Minnesota researchers along with a Lake Minnetonka marina owner and boat manufacturer are launching a project to figure out just how boat owners are spreading invasive species.

Some watercraft do not fully drain and hold some water in engines, bilges, ballasts and live wells, which can contain the microscopic zebra mussel larvae. Researchers will measure where and how much water gets left behind in different kinds of boats and figure out how long the larvae can survive. The idea is to help manufacturers redesign their boats and help inspectors know what to look for.

"And if a simple boat redesign could eliminate the problem, it just seems like a no-brainer," said Gabriel Jabbour, owner of Tonka Bay Marina, which is participating in the project.