Avoid Harmful Algae and Cyanobacteria
Harmful algae and cyanobacteria (sometimes called blue-green algae) can produce toxins (poisons) that can make people and animals sick and affect the environment. Learn more about them to keep you and your pets safe.
Algae and cyanobacteria are simple, plant-like organisms that live in the water. Algae and cyanobacteria can rapidly grow out of control, or “bloom,” when water is warm, slow-moving, and full of nutrients. Blooms can occur in fresh water, salt water, and brackish (a mixture of fresh and salt) water around the world. Blooms sometimes look like foam, scum, mats, or paint on the surface of the water. They can even make the water appear different colors, including green, blue, red, brown, or another color.
Blooms of algae or cyanobacteria can be harmful to people, animals, or the environment if they:
• produce toxins (poisons)
• become too dense
• use up the oxygen in the water or
• release harmful gases
Blooms can occur more often or become more severe with warmer water temperatures or if the amount of nutrients in the water increases. Levels of nutrients increase when fertilizer, sewage, or runoff from cities and industrial buildings get into the water.
How People and Animals Get Sick:
People and animals (including pets, livestock, and wildlife) can get sick when they have contact with water or food that contains certain types of algae, cyanobacteria, or their toxins.
People and animals can get sick if they:
• swim, wade, or play in or near contaminated water
• eat contaminated fish, shellfish or
• use contaminated drinking water
Illnesses and symptoms can vary depending on how a person or animal was exposed (came into contact with algae, cyanobacteria, or their toxins), how long they were exposed, which type of toxin was present, and how much toxin was present.
Symptoms can include:
• stomach pain, vomiting, or diarrhea
• skin, eye, nose, or throat irritation
• neurological symptoms (for example, muscle weakness, dizziness)
Animals can get very sick or even die quickly after exposure to harmful algae and cyanobacteria. Seek veterinary care immediately if your pets or livestock seem sick after going in or near water. Animals can die within hours to days of swallowing toxins. Animals are often the first affected, in part because they are more likely to swim in or drink from bodies of water that contain harmful algae or cyanobacteria.
Center for Disease Control (28/7/2021), Harmful Algal Bloom (HAB)-Associated Illness, Avoid Harmful Algae and Cyanobacteria, accessed 27 August 2021, <https://www.cdc.gov/habs/be-aware-habs.html>.