Harmful algal blooms are a large amount of microscopic photosynthesizing aquatic organisms that produce biotoxins. This type of vibrant green algae contains cyanobacteria and eukaryotic taxa. It also produces a visible algal scum on the surface of the water and causes taste and odor issues in drinking water. Cyanobacteria found in this algae can contribute to human health problems, such as, skin irritations from contact, gastrointestinal, respiratory, and neurological issues. It is also harmful to animals, mainly canines and livestock. The main causes of these algal blooms are fertilizers used in agricultural practices, urban runoff, and improper treatment of wastewater. Also, zebra and quagga mussels that have selective water filtration. In addition to the main causes, precipitation, wind, and temperature can aid in the growth of algal blooms. As these blooms decompose the water is depleted of oxygen, which results in fish mortalities. Although not all algal blooms are harmful, Lake Erie has become well known for its harmful algal bloom events that occur mostly in the Western basin of the lake. Researchers continue to test and monitor the water in effort to predict the blooms and prevent the harmful effects caused by it.