Outbreaks of an unusual and potentially toxic blue-green algae have been reported in at least five western Minnesota counties, including in Maplewood State Park in Otter Tail County, conservation officials said last week.

In addition to Otter Tail, algae outbreaks have been reported in Becker, Douglas, Pennington and Polk counties.

The blue-green algae can be toxic, although tests so far haven’t found toxic levels in any of the infested waterways, said Tim James, a project manager with the Minnesota Department of Natural Resources (DNR) in Detroit Lakes.

However, a similar outbreak several years ago on the Mud River near Grygla in Marshall County killed two dogs who were exposed to the algae.

“When in doubt, best stay out” of the water, James said.

James attributed the algae outbreaks to a hot, calm summer. Warm, still water provides favorable conditions for algae growth. James added that Minnesota has a longer growing season than it once did.

“Ice forms later and leaves earlier,” he said. “People are water skiing and swimming on Memorial Day now, when it used to be that people didn’t really go in the water until the Fourth of July.”

Is it due to possible global warming?

“I’ll let you attach that moniker to it,” James said. “The climatic conditions in Minnesota are very well documented. We have much more favorable conditions than we had in the past.”

The algae hit Thief River Falls hard last month, forming thick, slimy mats for about 2 miles on the Thief River, which runs through town. The water was very warm and stagnant, said Corey Hanson, a water quality coordinator with the Red Lake Watershed District. One local landowner reported a water temperature of 86 degrees on his fish finder.

“That’s very high for water,” Hanson said.

The city closed its swimming beach on the river and put up warning signs, but the outbreak has pretty much ended. However, the Pennington County Board has adopted a temporary no-wake ordinance through Nov. 1 for roughly 5 miles along the Thief River from Long’s Bridge to the county line.

“You don’t want to cause a panic, but you want to let people know it’s something to keep an eye on,” Hanson said. “There’s been more interest in this than anything we’ve ever done.”