Outbreaks of potentially harmful algae are a growing problem in waterways across the United States including Minnesota, according to a new report.

The Environmental Working Group, a nonprofit advocacy organization, used news reports and satellite imagery to track harmful algal blooms. The group found nearly 300 blooms recorded in lakes and rivers in 48 states since 2010.

The report also found that the problem apparently is getting worse. Last year, 169 blooms were reported in 40 states, compared to three in 2010.

Harmful algal blooms, sometimes known as blue-green algae, are technically not algae. They are a single-cell organism called cyanobacteria that can blanket a lake and sometimes look like bright-green pea soup.

Cyanobacteria sometimes produce toxins that can harm fish and marine life. They also are hazardous to humans and animals.

A blue-green algae bloom on Peltier Lake, near Lino Lakes, Minn., last summer. Dan Kraker | MPR News 2017

In Minnesota, blue-green algae blooms have been reported in several lakes in recent years, including Lake of the Woods, Carver Lake in Woodbury and Lake Cornelia in Edina.

The biggest contributor to algal blooms is polluted runoff from farms, said Craig Cox, senior vice president for agriculture and natural resources at the Environmental Working Group.

"The phosphorus that's applied in fertilizer or applied in manures can run off during rainfall events and find its way into streams and rivers and lakes," Cox said.

Lawn fertilizer and wastewater treatment plants also can contribute phosphorus.

Harmful algal blooms caught the nation's attention in 2014, when a large bloom in Lake Erie made the city of Toledo's water supply unsafe to drink for three days.

"This real crisis with drinking water is what really put these toxic algal blooms on map," Cox said.

The incident prompted the U.S. Environmental Protection Agency to set health advisory guidelines for two cyanobacteria toxins in drinking water. However, there are currently no enforceable legal limits.

Cox said more regulations are needed to reduce fertilizer and manure runoff from farms.

"By far, the best option is to prevent this contaminant from getting into waterways in the first place," he said.