The fight to keep invasive species from infesting more of Minnesota's lakes and rivers will ratchet up Thursday — and will affect virtually all 800,000 boat owners in the state.

That's when a law goes into effect requiring boaters to drain all livewells and bilges in their boats before they leave any lake or river. Currently boaters must drain their craft only after motoring on infested waters.

There's more: The new law also makes it illegal to even trailer a boat on a public road with its drain plug in. And it will be illegal to dump minnows, leeches, nightcrawlers or any other bait into waters.

The idea is to slow the spread of exotics like zebra mussels, spiny water fleas and Eurasian watermilfoil.

"We're trying to cover as many potential pathways as we can,'' said Jay Rendall, Department of Natural Resources invasive species program coordinator. "It's really important.''

"It makes everyone need to be aware of (the invasive issue) statewide, and not just on certain (infested) lakes,'' added Rendall. "It's simple: Drain all your water, take off all your plants, and you should be good to go.''

The change requiring boats being trailered to have their drain plugs removed or opened will make enforcement of the laws easier, Rendall said.

"We don't have to just sit at an access and watch people. If you're going down the road and your drain plug is in, it would be a violation.''

The law also clarifies the disposal of live bait.

"Now you can't dispose of bait in water, and, under littering laws, you can't dump it on the ground,'' said Rendall. "What we recommend is you put it in the trash or compost it at home.''

Anglers fishing on waters infested with zebra mussels or spiny water fleas — the DNR identifies these with signs at boat-launch sites — already must drain their portable bait containers when they leave a lake. If they want to keep the bait, they must replace the water with non-infested water.

The state has been criticized by some citizens and lake associations for not taking a more active response to what has been the gradual spread of exotic species. Zebra mussels and spiny water fleas could change the ecosystem of lakes, which could affect everything from fishing to tourism.

"People are passionate about it and want us to do more,'' Rendall said. "It's definitely a big issue.''

Besides the tightened laws, which was done by the Legislature, the DNR is ramping up its efforts this summer.

"We're increasing enforcement and inspections,'' Rendall said. "We've got 31 billboards in the state (devoted to invasive species threats). We're giving more grants to local groups for prevention efforts.''