What are algae?

Pond showing a green algal bloom

Algae are mostly aquatic, plant like organisms that can range in size from microscopic to giant kelp found in the ocean. Algae are photosynthetic organisms, meaning they use sunlight to process food and produce oxygen. In aquatic ecosystems, algae play a major role not only by producing oxygen but also making up the base of the food chain.

What are harmful algal blooms (HABs)?

Large growths of algae are called algal blooms and they can severely reduce or eliminate oxygen in the water, leading to illnesses or death of large numbers of fish. Blooms are considered harmful when they have detrimental effects on aquatic ecosystems, or human, livestock or pet health. Algal blooms caused by cyanobacteria, also known as blue-green algae, are harmful because they may produce toxins that can make people and animals sick if they come into contact with the polluted water, consume tainted fish or shellfish, or drink contaminated.

What are blue-green algae?

Blue-green algae are not actually algae, but cyanobacteria. Like algae, these bacteria can “bloom” when the conditions are right. Cyanobacteria are especially concerning because they are capable of producing toxins that can be harmful, even lethal, to humans, livestock and pets.

What causes HABs?

Blooms occur when weather conditions and an over-abundance of nutrients (nitrogen and phosphorus) in a waterbody create the perfect environment for rapid growth. Nutrient pollution is a national concern that is caused by excess nitrogen and phosphorus in the air and water. Nitrogen and phosphorus are nutrients that are natural parts of aquatic ecosystems. However, when a wide range of human activities cause too much nitrogen and phosphorus to enter the environment, the air and water can become polluted. Nutrient pollution has impacted our waterways for the past several decades, resulting in serious environmental and human health issues and impacting the economy. Too much nitrogen and phosphorus in the water causes algae to grow faster than ecosystems can handle. Sources of nutrients include wastewater and run-off from farm fields and lawns. HABs typically take place during summer and early fall when the weather is warm and water temperatures are high. However, blooms can occur any time of the year if conditions are right. For more information, visit EPA's Nutrient Pollution, Sources and Solutions webpage.

Where are HABs found?

Blooms can be found throughout Missouri. Lakes and ponds are the most likely waterbodies to experience blooms, but they also can occur in streams, especially if they are slow moving or pooled. 

How will I know if a HAB is present?

Unfortunately, you cannot tell if an algae bloom is toxic just by looking at it. Higher levels of toxins are typically associated with algae blooms that appear as thick foam or scum on the water’s surface. They can be bright green, blue-green, white, red or yellowish-brown in color. The water may look like pea soup or the surface may look as if paint has been spilled on the water. If you come across areas of thick algae, take precaution by avoiding water contact and keeping pets out of the water. As the cyanobacteria begin dying and decomposing they may release an unpleasant odor similar to rotting plants.

What kind of toxins do cyanobacteria produce?

Toxins produced by cyanobacteria are known as cyanotoxins. They can be produced by a wide variety of cyanobacteria species, some even producing more than one type of cyanotoxin. Scientist do not fully understand what causes cyanobacteria to start producing toxins. It could be an environmental change or need to out-compete other organisms in the waterbody for food or light. The most common toxins produced in Missouri are microcystins, cylindrospermopsin, anatoxins and saxitoxins. To learn more about these toxins, visit EPA's - The Most Commonly Found Cyanotoxins in the U.S.

When in doubt, stay out!