Freshwater Algae Blooms: Contributing Factors and Health Concerns Massachusetts Department of Public Health, Bureau of Environmental Health What are algae blooms? Algae blooms form when cyanobacteria (also known as blue-green algae), which are photosynthetic bacteria that grow in water, multiply quickly and form scums or mats on the surface of the water. Cyanobacteria are a natural part of the ecosystems of lakes and ponds, but can cause problems when they undergo explosive growth. Blooms in New England are most common in summer. Depending on the severity of the bloom the water could range from appearing slightly colored to resembling pea soup or paint. Blooms frequently appear blue or green but could be another color, such as brown or red. Algae blooms can cause odor and taste issues in the water, fish kills, and illness in humans and animals. Decomposing blooms can rob the water of the dissolved oxygen vital to fish and other aquatic life. In addition, certain species of cyanobacteria can manufacture toxins which pose a health risk to people and animals coming in contact with or ingesting the water. Contributing Factors Certain environmental conditions, such as warm weather, sunlight, and an abundance of nutrients in the water, are more favorable to the rapid growth of blue-green algae. Excess levels of nutrients in water bodies can come from anthropogenic, or human-related, sources. Phosphorus and nitrogen, which are found in human and animal waste and fertilizers, are two important nutrients used by blue-green algae in their growth. Examples of sources that can input large amounts of nutrients to water bodies are agricultural activities, leaking septic or sewer systems, stormwater runoff, lawn fertilizers, and pet and wildlife waste. People can lessen the inputs of these nutrients to water bodies by properly maintaining septic systems, planting or maintaining native vegetation around the water’s edge, using low- or no-phosphate dishwasher detergent, applying fertilizer correctly, and picking up pets’ waste. Do not feed birds or geese. It is also important to realize that most storm drains empty directly into water bodies without treatment. Never put or pour anything into a storm drain. Wash your car on your lawn or at a commercial car wash instead of on your driveway. Avoid fertilizing onto pavement or directly into a storm drain. Health Concerns Health concerns related to algal toxins vary depending on the type of exposure (contact or ingestion) and the concentrations of toxin present. Contact with high levels of cyanobacteria has been found to contribute to eye, ear, and skin irritation. Ingestion can lead to more serious health effects such as muscle cramps or twitching. If elevated levels of the algal toxin microcystin are present in the water and ingested, serious liver damage can result. Exposure to elevated levels of the algal toxin anatoxin can cause serious neurological damage. Small children and pets are more susceptible than adults to the effects of toxins. Livestock and pet deaths from ingestion of algal toxins have been reported. If you see water that appears to have an algae bloom, do not come into contact with or ingest the water. Treating water by boiling does not get rid of any toxins present. Prevent contact and ingestion by kids and pets. Dogs can get very ill and even die from licking algae out of their fur. Rinse dogs off immediately if they come into contact with water with an algae scum or bloom. MDPH Guidelines MDPH reviewed World Health Organization guidance and current scientific literature in order to develop a protocol for evaluating potential health concerns related to the presence of cyanobacteria. The ability of cyanobacteria to multiply quickly makes monitoring their numbers important. Because health risks rise with cell counts, the goal of any monitoring plan is to be able to take action before levels are reached that pose health risks. MDPH recommends an advisory or closure when: A visible scum or mat layer is present The blue-green algal cell count exceeds 70,000 cells/milliliter The microcystin level of lysed cells exceeds 14 parts per billion (ppb) For More Information or To Report a Bloom Vanessa Yandell is the Algae Project Coordinator for the Massachusetts Department of Public Health, Bureau of Environmental Health Phone: Website: Additional Resources: U.S. Centers for Disease Control and Prevention: U.S. Environmental Protection Agency: