In the winter, you avoid yellow snow. In the summer, don't touch green algae. The Army Corp of Engineers says a potentially harmful green algae bloom has developed on the Illinois River – though its location isn't made clear.
The Corps advises you to keep kids and pets away from bright, blue-green algae. It's really cyanobacteria. If you touch or swallow it, skin or even throat irritation, flu-like symptoms and gastrointestinal illness may develop.