Water levels have returned to nearly normal on Minnesota waterways, most no-wake restrictions have been lifted, and boaters are back on the water.

So, too, are state conservation officers, seeking to slow the spread of aquatic invasive species (AIS).

"Now that boating season is picking up, we're going to try to ramp up [enforcement]'' said Capt. Greg Salo, Department of Natural Resources enforcement manager.

The DNR had planned to conduct 36 random check stations this summer — twice as many as last year — in hopes of reducing a violation rate deemed too high. At those sites, motorists with boats are directed to pull over for mandatory inspections. But the poor boating weather this spring and summer hindered those efforts.

"Lot of spots where we normally set up were under water,'' Salo said. And boaters stayed home.

Officers have conducted about 15 random checks so far, including several last weekend. And more will be done before Labor Day. Officers also continue to check boats as part of their normal duties.

Chris Hattendorf of Ashton, Iowa, with his 46-pound, 14-ounce winning catfish from last weekend’s Franklin Catfish Derby Days contest.

So far, conservation officers have issued 232 tickets and 516 warnings for AIS violations. The No. 1 violation is for transporting a boat with the drain plug in, Salo said. Compliance varies around the state. But the bottom line is too many boaters continue to violate the law, threatening to heighten the spread of invasive species to more lakes.

"Anglers who are nomadic and move around are usually good with compliance,'' Salo said. "It tends to be recreational boaters that have bought a boat in the last two or three years and are taking the kids tubing — that's where we are seeing a lot of our violations.''

The violation rate at the random check stations was 20 percent last year, and 26 percent earlier this season, but has been falling.

"The violation rate is still too high,'' Salo said.

Catfish contest

Concern over high water apparently kept attendance down at the Franklin Catfish Derby Days contest last weekend. "I think with the river so high they were afraid they wouldn't be able to find a spot to fish,'' organizer Brian Pederson said. "We had 203 anglers, where we usually have around 300.'' The winning fish was a monster 46-pound, 14-ounce catfish caught by Chris Hattendorf of Ashton, Iowa.

Doug Smith • doug.smith@startribune.com