Have you ever experienced strange colors or smells in your pond or seen them in a lake? Have you ever wondered what might have caused them? Cyanobacteria, often called blue-green algae, are bacteria that are found naturally in lakes, ponds, and slow-moving streams.

They are often called blue-green algae because they contain pigments that allow them to photosynthesize, like plants, and give them a blue-green color, and can be filamentous like other algae.

Given the right water conditions, which are generally seen in the warmer summer months, cyanobacteria can dramatically increase in number, or “bloom.”

Not all algal blooms produce toxins, although fish-kills often accompany algal blooms because of depleted oxygen in the water when algae begin to die and decompose. Nor do scientists fully understand what causes the same species of algae to produce toxin during one bloom and not produce toxin during the next.

Algae blooms can look like foam, scum, or mats on the surface of freshwater lakes and ponds. They can also make the water take on a color (blue, green or brownish) or a pea-soup appearance.

Algae blooms are not all caused by cyanobacteria, however, the blooms caused by cyanobacteria can be more than a nuisance. These blooms are called Harmful Algal Blooms (HABs) and can make you or your pets and animals ill.

Cyanobacterial HABs can be foam, mats or scum and their color can range from blue to blue/green, bright green, brown, or red and may even look like paint floating on the water. While not all species are capable of producing toxins and causing HABs, some are. The toxins are produced in the cells of the cyanobacteria and are released when the cells begin to die.

Odors associated with the blooms can be described as “earthy” or “musty.” They are caused by geosmin in the water. Humans are generally very sensitive to that smell. While the odors themselves are not toxic, fine droplets of water “whipped up” by motor boats, water skis or irrigation activities can cause misting. Breathing the water droplets can cause illness.

HABs can produce neurotoxins (which affect the nervous system) and hepatotoxins (which affect the liver). The toxins can also cause skin problems. These toxins can have effects on the health of people and animals that come into contact with water where HABs are present in high numbers.

And while both humans and pets can get sick from exposure to cyanobacteria toxins, the type of cyanobacteria, the levels in the water and the type of contact will influence how illness develops after contact.

So what type of illness might result from different types of contact with water containing these toxins?--

-- Contact with the skin may cause rashes, hives, or skin blisters (especially on the lips and under swimsuits).

-- Breathing suspended water droplets (mist) from water-related recreational activities and/or lawn irrigation can cause runny eyes and noses, a sore throat, asthma-like symptoms, or allergic reactions.

-- Swallowing HAB-contaminated water can cause: Acute (immediate), severe diarrhea and vomiting; Liver toxicity (abnormal liver function, abdominal pain, diarrhea and vomiting); Kidney toxicity; Neurotoxicity (weakness, salivation, tingly fingers, numbness, dizziness, difficulties breathing, death)

To protect yourself, your family and your pets:

-- Avoid direct contact with the lake water or aerosolizing the water. (Don’t swim, water-ski, tube, or boat at high speeds)

-- Don’t use HAB-impacted water for irrigation or watering lawns or gardens.

-- Report unpleasant tastes or smells in your drinking water to your local water utility.

-- Follow posted water body advisories.

If you do come into contact with the HAB contaminated water, you or your pets should rinse off with clean, fresh water as soon as possible. Pets that have been swimming in an area with a HAB can swallow toxins by licking their fur after leaving the water.

If you think you, your pet, or your livestock might have been poisoned by toxic HAB, remove people or animals from the exposure and seek medical treatment ASAP, especially if symptoms occur.

For additional information visit:

-- What Are The Dangers Of Harmful Algal Blooms?  FAQ

-- What Causes Harmful Algal Blooms? FAQ

-- Harmful Algal Blooms - Ohio Department of Health

-- Photo Gallery Of Green And Blue-Green Algae

(Written By: Diane Oleson, Natural Resources Educator, Renewable Natural Resources Team, Penn State Extension, York County, and reprinted from Penn State Extension's Watershed Winds newsletter.)

8/19/2013