Algae are found in all salt and freshwaters worldwide. Although algae are very simple in their structure and sometimes consist only of a single cell floating in water, they are tremendously important for the health of our planet. Algae provide the base of food chains that support whales, seals, sharks and all other marine organisms in the oceans. In freshwaters, they also support food chains that lead to animals as diverse as bass, bald eagles and grizzly bears. Another essential role of algae is that they produce between 40-50% of the oxygen that we breathe through the process of photosynthesis!
Algae grow rapidly and reproduce primarily by cell division and by the formation of spores. They do not produce flowers or seeds. Most of the time people don’t notice them, even though they are present in most bodies of water from bird baths to large lakes. Under certain circumstances, algae grow so prolifically that we do notice them. This is when water turns pea-soup green, or when masses of what is commonly called “moss” float on the surface of the water. It is these algae that often need to be managed because of the problems they can cause.
In addition to being unsightly, excessive algal growth (often called blooms) can lead to fish kills. This happens when the algae in a body of water die (crash) all at once. Crashes can be caused by a variety of factors including cell aging, nutrient depletion or sudden changes in weather, such as a shift in water temperature or a period of prolonged cloudiness. Bacteria and fungi that break down the dead algal cells (organic matter) require large amounts of oxygen; as algae decompose, oxygen in the water is depleted, which results in oxygen-starved and dying fish.
Wisconsin Department of Natural Resources individual chemical fact sheets: