For four years, Maureen Ziskovsky has been politely asking Minnesotans at lakes around the Twin Cities to dump their bait and rinse seaweed off their boats. Usually, they say yes. But sometimes they refuse, increasing the chances that zebra mussels will spread to yet another lake the next time they use their boat.

But now she has the law on her side. Starting this weekend, she's one of 17 specially trained officers with the Department of Natural Resources armed with new authority to require the inspection and decontamination of boats -- and to turn away boat owners who refuse to comply.

The added authority, she said, is huge. "Now we can say, 'You cannot launch,'" Ziskovsky said Friday morning as she watched dozens of boats coming and going at the boat launch on Gray's Bay in Lake Minnetonka.

It's the latest escalation in the state's decade-long effort to thwart the spread of zebra mussels, an invasive species that has infested at least 20 of Minnesota's more popular and intensively used lakes.

The mussels from central Europe were first discovered in the Great Lakes in the late 1980s, and in Minnesota waters a few years later. They have no natural enemies in North America, and their populations often explode shortly after they become established in new waters.

At their earliest stage, they are microscopic and float freely, finding their way into bait buckets and getting caught up in vegetation that attaches to trailers and boats. As adults, they attach to docks, hulls and other hard surfaces by the millions, starving out native mussels and changing fish habitat. After they die, their razor-sharp shells litter beaches and lakefronts.

This year, just as the mussels were found for the first time in Lake Minnetonka, the Legislature nearly doubled the DNR's budget for the inspection program to $1.9 million.

That helped purchase three new high-pressure washing units, which can remove zebra mussels from boat hulls, trailers and bait wells that harbor invasive species. It also gives the DNR inspectors and conservation officers authority to turn boaters away, cancel their boat registration for a year or even cite them with a misdemeanor for more serious infractions.

For now, DNR officials said, the inspectors and boat washing units will be concentrated on boats coming out of infested lakes, including Minnetonka, Mille Lacs and Pelican Lake. Later, they will likely move to popular lakes that have not been infested. There, boats and trailers going into the lakes will be inspected for vegetation and mud that they carry from other lakes.

"The majority of boats won't need to be decontaminated," said Luke Skinner, the agency's supervisor for invasive water species, in a statement released Friday. "Only boats that don't pass an inspection will need to be decontaminated with the new equipment, and we suspect there won't be too many of them on any given day."

Never-ending battle

But in the Land of 10,000 Lakes, 3,000 public boat ramps and 866,000 registered boats, there will never be enough inspectors and boat washers to go around, Skinner said. To stop the spread, boat owners must adopt a routine of checking, rinsing and draining their own boats.

They "are our first line of defense," Skinner said. "For us, this is a culture change."

Doug Jensen, a specialist on invasive species at the University of Minnesota's Sea Grant program in Duluth, said that culture change is well on its way. Surveys of boat owners show a growing willingness to take action, rising from 70 percent in 1994 to 99 percent in 2006 and 2007, he said. "We know that attitude has changed significantly," he said.

That attitude was on display Friday at Gray's Bay as a steady stream of boat owners pulled their boats in and out of the water, stopping to watch the DNR inspectors run the high-pressure washer around and under the hulls.

"If I have time to do this," said boat owner Mark White, waving his hand toward the sparkling water, "I have time to do that."

Josephine Marcotty • 612-673-7394