High levels of nitrogen and phosphorus reached many of Iowa’s lakes this spring after heavy rains caused significant runoff from farmland. Those chemicals, in combination with the recent stretch of sunny days, have prompted a warning of a possible health concern.

Susan Heathcote, with the Iowa Environmental Council, says harmful algae is in full bloom in some waterways and it’s easy to spot. “There’s an unusual green coloring to the lake, often it looks like pea soup or like paint has been spilled,” Heathcote says.

Exposure to blue-green algae can cause skin rashes or breathing difficulties, especially in children. “The algae will form mats on the top of the water, it kind of floats. It looks bad and often has a bad odor associated with it,” Heathcote says.

Pet owners should also be careful not to let their dog swim in the water if it looks or smells bad. “This is something to be really aware of if you have a pet that likes the water,” Heathcote says. “If they get in the water, make sure you wash them off afterward and if they have the scum and algae on their fur, don’t let them lick their fur.”

The Iowa Department of Natural Resources monitors all 39 of the state-owned beaches and results can be found on the agency’s website. This weekend, swimming is not recommended at Back Bone Lake near Strawberry Point, Beed’s Lake near Hampton and Geode Lake near Mount Pleasant.