JANESVILLE, Wis. — Health officials in Rock County, Wis. noticed blue-green algae blooms in the Rock River and Lake Koshkonong earlier this week, including at the Traxler Park Boat Launch in Janesville. 

“It does typically drift to the shore, because of the way the water currents happen,” said Jessica Turner, a spokesperson with the Rock County Public Health Department. 

The shore is where most swimmers get into the water, which is something the health department is warning about, as blue-green algae can cause serious health problems. 

“[It can cause] irritation to the eyes, nose, you might have some respiratory symptoms,” Turner said. "A little more severe, you might have some vomiting, diarrhea."

Dogs and other pets are more prone to serious complications, such as nervous system issues, convulsions, and paralysis. They could also die from blue-green algae because animals are more likely to ingest or drink the water. 

Turner said the high heat and humidity, and very light winds, are what’s causing the algae to grow in more places right now. 

“So, that makes this week, and it’s looking like next week will be good times for these blue-green algae to occur,” Turner said. 

Not all blue-green Algae is toxic, though. However, you can’t tell if it’s toxic or not just by looking at it. 

That’s why local health departments want to make sure residents are following their warnings to not swim in the water if the algae is present. 

“Yeah, that’s the best rule of thumb,” Turner said. "Just make sure that you wash off really well; don’t ingest the water; don’t be swimming in water where you’re seeing this occur."

Most local health departments post these warnings on their website, so you can know before you go, to ensure confidence you are swimming in safe water.