The Rock County Health Department says a potentially dangerous algae has been found on Lake Koshkonong. Environmental Health Director Rick Wietersen warns Blue-Green Algae can be toxic to people and pets. Wietersen advises against swimming or risking ingestion in areas that may have the algae, especially if there’s a floating scum layer colored green, blue, or even resembles white paint. He says if you do come in contact with the algae to rinse off as soon as possible. He also says conditions are favorable for development of the algae on other area waterways.