First-ever random roadside checks of Minnesota boaters planned for this spring and early summer -- part of a crackdown to slow the spread of invasive species -- have been delayed because of legal concerns by some county attorneys.

"Some are just not buying into whether the legal authority is there," said Jim Konrad, Department of Natural Resources enforcement chief.

Otter Tail County Attorney David Hauser is among those who have concerns.

"Our Supreme Court has found random stops for DWI are not constitutional," Hauser said. "We've asked the DNR, before we proceed with these stops, let's look at this."

Said Hauser: "We want to enforce the laws, but in a legal and constitutional manner. We don't want to run roughshod over peoples' rights."

Mark Rubin, St. Louis County Attorney, said his office also is looking at the law. "We want to make sure it's something they can do," he said.

Konrad said he believes a 2011 state law gives DNR conservation officers authority to do random checks, where motorists towing boats would be directed to an inspection station. That law made compliance with the inspections an "express condition" of operating or transporting boats and other water-related equipment.

But Konrad said the agency hasn't begun the program because local county attorneys would prosecute cases that result from the stops, so their cooperation is essential. "If we don't have buy-in from the county attorney, we're out of business," he said.

Two initial roadside checks that had been scheduled for last week were canceled. "It's a little disappointing, but we feel we can work through it," Konrad said.

He is sending letters to county attorneys stating why the DNR believes it has the legal authority for the random stops, and he hopes to have the issue resolved in time to begin the program by the July 4th holiday.

The plan is to target only boaters, he said, not other motorists, and minimize inconvenience.

"We want to make sure we're not more intrusive than we have to be," Konrad said.

Hauser said the 2011 law apparently allows officers to do the checks, but only in certain areas. It says conservation officers may utilize check stations "in locations, or in proximity to locations, where watercraft ... [are] placed into or removed from waters."

The random stops break new ground for the state's 2.3 million boaters. The DNR conducted random roadside checks for game and fish violations until the mid-1990s, when the state Supreme Court ruled that State Patrol sobriety checkpoints set up to nab drunken drivers without probable cause violated the state Constitution.

Konrad said the statute is modeled after laws in other states. Still, ordering motorists to pull over for a boat inspection is likely to upset some people, he acknowledged.

"We kind of expect there will be a challenge," he said. "We anticipate it would be upheld."

Konrad said the goal will be to move boaters through the inspection as quickly as possible. Preventing the spread of invasive species, such as Eurasian water milfoil or zebra mussels, to the state's lakes and rivers is worth the minor inconvenience, he said.

"We've been empowered to do it, and our intent is to move forward," he said.

Meanwhile, Konrad noted that conservation officers are reporting that 20 percent of those they check are violating invasive species laws. "That scares me," he said.

Beginning July 1, fines for those caught violating the invasive species laws -- which currently range from $50 to $250 -- will double to $100 to $500.

Doug Smith • dsmith@startribune.com