Blue-green algae, also known as cyanobacteria, can produce toxins that pose a danger to public health, said Kait Reinl, research coordinator at the National Oceanic and Atmospheric Administration’s Lake Superior National Estuarine Reserve in Superior, Wisconsin. Symptoms from exposure include stomach cramps, diarrhea, vomiting, headache, muscle weakness, fever and difficulty breathing, according to the Wisconsin DNR. Pets and children are particularly at risk.