EDITOR'S NOTE: This series gives background information on algal blooms, the problems they create and what causes them. Check out the infographic about algal blooms' growing threat, what causes them and hot spots around the US.
Algae are microscopic phytoplankton such as bacteria and dinoflagellates that use photosynthesis to turn sunlight into energy. These microorganisms are naturally occurring and live in all types of water, from fresh to salt to brackish (which is a mix of fresh and salt). Algae are common in water bodies where they consume carbon and nutrients such as phosphorus and nitrogen.
When water reaches the right mix of sunlight, temperature, low water flows and excessive amounts of nutrients - the latter process called eutrophication - algae can multiply very quickly and turn into a "bloom." Nutrients, like nitrogen and phosphorus that are essential for plant growth, are beneficial in lower levels, but in overabundance they become pollution and often cause super-charged algal growth. (Excess nutrients can come from a lot of different sources, from synthetic fertilizer runoff to factory farm manure lagoon leaks to leaky septic systems - and more.)
When the algae die and are gobbled up by bacteria, they deplete the water of oxygen, a state called hypoxia. Hypoxic waters result in dead zones, which are harmful to aquatic life which can't survive in the low oxygen conditions. Aquatic species like fish are forced to flee dead zones while shellfish and bottom feeding creatures who can't escape die. Ecosystems are devastated by dead zones triggered by algal blooms, whether in small lakes to giant swathes of ocean.
The Many Colors of Algae and Their Potential Hazards
Harmful algal blooms (HABs) are also seriously harmful because of the vast array of biotoxins that they can produce which can poison humans, land and aquatic mammals, fish, shellfish and other aquatic species. There is a solid understanding about the central causes of algal blooms, although some uncertainty regarding the precise role and proportion of nutrients such as nitrogen and phosphorus remain. Even if the specific mechanism that activates these toxic - and sometimes foul-smelling - compounds are still being identified, scientists are deeply immersed in finding the answers in this fast-growing field of research.
One of the more notorious recent cases was the shutdown of the Toledo, Ohio drinking water supply during a particularly bad HAB outbreak in Lake Erie in 2014. Over 500,000 people went without tap water for five days as the city's water system cleared the cyanobacteria toxin, microcystin, from the supply.
Not only are these toxins unsafe to for humans to drink and to eat if they are present in fish or shellfish, but they can even be harmful to the touch and can cause skin irritation or nervous system problems. In every case, it's best for you and your pets (especially dogs) to stay of water that that appears to have an algal bloom.
There are many types of HABs, some of which can be identified by the colors they make in water. In the infographic below you can see the life cycle of an algal bloom, a few common algae types and the potential hazards they pose if toxins are present. (Click to see a larger version.)