Cyanobacteria are a group of bacteria found throughout the world. They grow in any type of water (fresh, brackish, or marine) and are photosynthetic: They use sunlight to create food and survive. Normally microscopic, cyanobacteria can become clearly visible in warm, nutrient-rich environments, which allow them to grow quickly and “bloom” in lakes and other bodies of water. These bacteria are commonly known as “blue-green algae” because of their color, texture, and aquatic location, but they’re not plants like true algae.
Cyanobacteria Blooms
Blooms of cyanobacteria — when the population of cyanobacteria explodes — typically occur in still or slow-moving water, such as lakes, ponds, and weak streams, when the water is warm, gets plenty of sunlight, and is rich in nutrients like phosphorous and nitrogen. In the United States, these blooms occur most often in summer and early fall, although they can occur any time of year, according to the Centers for Disease Control and Prevention (CDC). Because most cyanobacteria species float in water, blooms often appear as foam, scum, or mats on the water’s surface, and can cause clear water to become cloudy. Though typically blue-green in color, cyanobacteria blooms can also be blue, bright green, brown, or red, resembling paint floating on the water. In some cases, cyanobacteria blooms don’t affect the water’s appearance, making it difficult to know if a bloom is occurring. At the end of a bloom, when the cyanobacteria are dying off, the water may smell bad.
Harmful Algal Blooms (HABs)
Cyanobacteria can be helpful by providing nutrients to plants such as rice and beans. However, cyanobacteria blooms can also be dangerous. Cyanobacterial harmful algal blooms — known as HABs or CyanoHABs — can use up the oxygen in water and block sunlight that freshwater plants and animals need to survive. Some cyanobacteria also produce potent toxins, called cyanotoxins, during CyanoHABs. In the United States, the most common cyanotoxin-producing varieties are Microcystis, Anabaena, and Oscillatoria, which produce toxins in the microcystin, cylindrospermopsin, anatoxin, and saxitoxin classes, according to the Environmental Protection Agency (EPA).
Health Effects of Cyanotoxins
Exposure to cyanotoxins, caused by drinking or swimming in contaminated water, or breathing air containing cyanobacteria or their toxins, can affect the skin, nervous system, and liver. A wide range of symptoms can develop from cyanotoxin exposure, including:
Skin irritation and rashesStomach crampsNausea and vomitingDiarrheaFeverHeadacheSore throatMuscle and joint painMouth blisters and ulcersAllergic responsesTrouble breathingBurning or tingling in fingers and toesDrowsinessSlurred speechIncreased salivation
Life-threatening liver damage may also develop in people exposed to cyanobacteria through contaminated dialysis water. Dogs often become victims of cyanobacteria blooms when they swim in or drink contaminated water. Cyanobacteria blooms killed approximately 100 dogs between 2002 and 2012, according to a 2013 CDC-led study in the journal Toxins. However, this figure most likely underestimates the true number of deaths, because the CDC only surveyed 13 states.
