Algal Blooms & Toxin Production

Algae are important and necessary components to aquatic ecosystems. As primary producers that create their own food from the sun, they serve as the base of many food chains. As a result, they can control ecosystem structure – which organisms are there – and ecosystem function – what those organisms do. Therefore, algae can influence what services our waterways can provide such as being a source for drinking water and recreation.

Too Much of a Good Thing

While algae are important to ecosystems, they can also cause multiple issues when they grow in large amounts. Nutrients can control algal growth. Increased nutrient input into waterways has led to a larger food source for algae to grow and often bloom in great numbers. Algal blooms can result in decreased aesthetics, fish kills – large amounts of fish dying at once, loss of recreational use, and impaired drinking water. For example, large amounts of algae in a single bloom can use up a majority of the oxygen available in the water when they die off because microbes that break them down need oxygen to complete that process. Less oxygen is then available for fish, which can cause large fish kills.

In addition to algal blooms creating issues with depleted oxygen and aesthetics, harmful algal blooms (HABs) can also be an issue for public health. Several different types of algae can produce toxins that are harmful to people, pets, and other aquatic life. For example, a type of algae called dinoflagellates can produce red tides that make the Florida Gulf Coast unsafe for swimming, kill off fish, and make some shellfish unsafe to eat.

The possibly more commonly known HABs are produced by cyanobacteria, which are actually microscopic bacteria, and not algae at all. However, these organisms are often referred to as “blue-green algae.” Cyanobacteria can produce several types of toxins that can have effects on different organ systems in organisms. Below are examples of the main toxins found in aquatic systems in the United States:

  • Microcystins – Liver and kidney
  • Cylindrospermopsins – Liver and kidney
  • Anatoxin – Nervous System
  • Saxitoxin – Nervous System
  • Aplysiatoxin – Skin

For the most part, toxins are made within the cell and are released into the environment upon cell death and the resulting cell lysis. An exception to this is Cylindrospermopsin, which can occur both inside and outside the cell. Exposure to these toxins have been known to cause pets and people become physically sick. The presence of cyanobacteria in surface water used for drinking water also has the potential to result in costly management strategies to eliminate possible toxins in the water that people drink.

Why Are Toxins Produced?

Currently, the exact mechanism that causes cyanobacteria to produce toxins is not well understood. Specifically, the toxin production in cyanobacteria is costly from a biology standpoint in that it takes several molecules of energy to create toxins in this small organism. Thus, production of toxins must serve an important purpose in the organisms’ survival. There are several hypotheses as to why cyanobacteria produce toxins. Below are a few examples:

  • Genetics – Only certain strains of cyanobacteria are capable of toxin production.
  • Temperature – Toxin production is temperature dependent, with higher temperatures driving growth of cells that produce toxins over those that don’t.
  • Nutrient availability – Cyanobacteria may produce toxins in response to the availability of certain nutrients such as forms of nitrogen and phosphorus.

Why Monitor Algal Blooms and Toxin Production?

Monitoring for algal blooms and toxins helps us protect public health and our water resources. Through monitoring we can identify blooms when they happen, and alert the public through advisories and restrictions of areas. Also, through this monitoring we can better understand the mechanism behind what causes toxin production in cyanobacteria – a mechanism that isn’t completely understood. This knowledge will help inform management practices as well as treatment for drinking water professionals.

Water Resource Professionals in Indiana Focusing on Algal Blooms and Toxin Research and Monitoring:

    • Cyndi Wagner (Indiana Department of Environmental Management)
    • Mitt Denney (Indiana Department of Environmental Management)
    • Greg Druschal (Indiana University-Purdue University, Indianapolis Center for Earth and Environmental Science)
    • Nate Bosch (Grace College)

Related Resources

Center for Earth and Environmental Science, 2017. Algal Toxicology and Dynamics. Accessed August 10, 2017 at

Graham, J.L., 2007. United States Geological Survey: Harmful Algal Blooms. Accessed August 10, 2017 at

Indiana Department of Environmental Management, n.d. Blue Green Algae Fact Sheet. Accessed August, 10 2017 at

National Oceanic and Atmospheric Administration, n.d. Harmful Algal Blooms: Tiny Organisms with a Toxic Punch. Accessed August 10, 2017 at