If you recall, back in 2019, The Illinois Environmental Protection Agency (IEPA) and the Illinois Department of Public Health (IDPH) were asking Illinois residents to be more vigilant about where they boat, ski, and swim over the summer due to blue-green algae "blooms" that are occurring in Illinois' lakes and rivers.
If you guessed "the two-legged kind," you would technically be correct. We humans pose a lot more danger to each other than animals do, but we're talking about four legs (mostly), fur (sometimes), and fangs here.