State of Oklahoma officials say they know of 46 people who have gotten sick from blue-green algae.
The symptoms are flu-like--including fever, body aches, vomiting and diarrhea.
The toxin thrives in warm, stagnant water.
If you want to check the conditions at your favorite lake, click here to go to the Travel OK website.
If you swim in an area that may have blue-green algae, be sure to rinse off with soap and fresh water afterward. And remember, the blooms can be toxic to pets.