Algae are simple aquatic plants that we often find growing in bodies of water throughout Illinois. We often associate algae with a slimy feeling that makes our ponds and lakes less attractive; it gets stuck on our fishing poles, and it makes swimming less enjoyable. Although algae often get a negative rep, it does produce more than 50% of oxygen in our atmosphere. However, like most things, algae are beneficial under the right circumstances.  Excessive algae growth can cause taste and odor problems with drinking water and can even kill fish by limiting oxygen and food.