Most of Minnesota’s 2.3 million boaters know they must remove their boat’s drain plug after they tow their craft from the water to prevent the spread of aquatic invasive species.

And those plugs can’t be reinstalled until a boater is readying to launch at a landing.

The problem is remembering to do that.

Some boaters have done so only after noticing water flooding into their boats.

“I’ve come close [to forgetting], and I’ve worried about it, but I haven’t actually done it,’’ said avid boater Jon Harkness of Maple Grove.

But the thought of accidentally sinking his 18-foot runabout got him ruminating. Harkness invented a device that he says is an almost foolproof way to store a boat plug and also remember to reinstall it.

“It just kind of came to me,’’ he said. “I thought why not store it in a place where you also retain your kill switch tether, so you can’t start your engine without remembering to put your plug in?’’

The result: Plug Dock, a small plastic device that holds both the drain plug and the kill-switch tether. It’s attached with adhesive to a conspicuous place on a boat.

“Every boater who removes his drain plug is faced with two questions: Where am I going to store it, and how will I remember to put it back when I launch my boat?’’ Harkness said. “This little chunk of plastic answers both questions.’’

Harkness, a patent attorney, and his partner, Dan Martinson of Medina, who is in the plastics business, started producing and peddling the devices this spring.

Wildlife Forever, a nonprofit group based in Brooklyn Center, is helping distribute them to lake associations and government agencies as part of the Stop Aquatic Hitchhikers campaign, with the idea that they be given away free at boat inspection sites.

They’re also available for purchase at Hallberg Marine in Wyoming, Minn., and through the company’s website, www.plugdock.com.

Harkness thinks he has invented a better mousetrap, and hopes to get the devices — which sell for about $10 — into other retail outlets. They hold either a half-inch threaded plug or 1-inch expandable rubber plug.

“We feel it’s a neat product to remind folks to pull their plug — it’s a no-brainer concept,’’ said Pat Conzemius, Wildlife Forever conservation director.

Wildlife Forever has started offering Plug Docks at discount to lake associations.

“We’re not in this to make money, we want to get folks to change their behavior,’’ Conzemius said.

Minnesota Sea Grant in Duluth bought some that will be distributed in the Duluth and Lake Superior area, Conzemius said.

More random checks

Whether the devices sell, or help improve compliance with the law, remains to be seen.

But despite intense publicity about the drain-plug law since it was passed in 2010 — including billboards, TV, radio and print advertisements and beefed-up enforcement — some boaters still haven’t gotten the message. Conservation officers issued several citations last weekend on the fishing opener.

And last year, officers reported a 20 percent violation rate at 18 roadside check stations where boaters were pulled over and checked for aquatic invasive species compliance. That was an improvement from the 31 percent violation rate in 2012.

“We are improving, yes, but we still have a ways to go,’’ said Phil Meier, Department of Natural Resources enforcement operations manager. “It’s frustrating for us to see that violation rate.’’

The violation rate was a bit better — 14 percent — during nearly 8,000 routine checks made by conservation officers during their patrols last year. But Meier said the agency believes the violation rate at the check stations — where boaters are forced to pull over to be checked — more accurately reflects the true compliance level.

This season, the DNR will operate 36 check stations — twice as many as last year — in an effort to boost compliance.

“Our goal is not to write tickets, our goal is to prevent any new infestations,’’ Meier said.

The DNR doesn’t announce where those check stations will be. They are done on roads or highways leading to lake or river accesses, where motorists towing boats can be safely pulled over.

“For the most part, people are happy to see us out there,’’ Meier said.

Meanwhile, the DNR also will have 146 boat inspectors and 23 boat decontamination units at landings this summer, said Adam Doll, DNR acting watercraft inspection coordinator.