Frequently Asked Questions: Cyanobacterial (Blue-green algae) Blooms

Overview

Algae are found in all aquatic systems and are an essential food source for many organisms. Algal blooms that cause adverse effects are known as Harmful Algal Blooms (HABs). When favorable environmental conditions exist, algae can reproduce rapidly and form blooms that appear as surface scums, water discoloration, or both. Blooms also cause major changes in water chemistry, including high pH and dramatic swings in dissolved oxygen. Lack of oxygen created by decomposing algal blooms sometimes results in fish kills and other aquatic life impacts.

Some algae, especially blue-green algae, can produce toxins. These toxins have been linked to adverse health effects in wildlife, domestic pets, and humans. The North Carolina Department of Environmental Quality Division of Water Resources currently tests samples for microcystin, one of the most common and well-studied algal toxins. Information on how to report or track algal blooms in North Carolina can be found online: Algal Blooms. 

Frequently Asked Questions

What are cyanobacteria?

Cyanobacteria, commonly called blue-green algae, are naturally occurring algae present in most fresh waterbodies across North Carolina. Under certain environmental conditions, cyanobacteria can reproduce rapidly to form a cyanobacterial bloom. Blooms are most common during summer months when bright sunlight, warm temperatures and increased nutrient availability promote cyanobacterial growth. Some cyanobacterial blooms are able to produce toxins, called cyanotoxins, which can cause illness in humans and animals that come into contact with water affected by a bloom.

What does a cyanobacterial bloom look like?

Cyanobacterial blooms may or may not be easily visible. Blooms can form below the water’s surface or along the bottom. Cyanobacterial blooms that form near the water’s surface can cause water discoloration, surface scums (often described as “spilled paint”) or floating clumps or mats. Blooms can appear bright green, blue, red or brown. As cyanobacteria in a bloom begin to die, they may produce a strong, foul odor and turn milky blue in color.

How do I report a bloom?

Suspected algal blooms can be reported to the N.C. Division of Water Resources through the Fish Kill/Algal Bloom Reporting Survey or by contacting the nearest regional office. Reports are reviewed during normal business hours, and further evaluation is prioritized by event severity and available resources.

When does the state test for cyanobacteria/cyanotoxins?

The NCDEQ Division of Water Resources Algae Lab tests samples for microcystin, one of the most common and well-studied algal toxins. The lab conducts testing in the spring, summer and fall seasons in cases of suspected cyanobacteria as resources allow. 

How can I protect myself, family and pets from cyanobacterial blooms?

The N.C. Department of Health and Human Services (DHHS) recommends the following guidelines to safeguard people and pets from cyanobacterial blooms:

• Keep children and pets away from waters that appear discolored or scummy.
• Do not handle or touch large accumulations (“scums” or mats) of algae.
• Do not water ski or jet ski over algal mats.
• Do not use scummy water for cleaning or irrigation.
• If you accidently come into contact with an algal bloom, wash thoroughly.
• If your pet appears to stumble, stagger or collapse after being in a pond, lake or river, seek veterinary care immediately.
• If your child appears ill after being in waters containing a bloom, seek medical care immediately.
• If you are unsure whether or not a bloom is present, it is best to stay out of the water.

How can I have my water tested for cyanobacteria/cyanotoxins?

Testing for cyanobacteria and cyanotoxins is specialized and can only be done by a few laboratories. At-home test kits for algal toxins are commercially available through private vendors. See the U.S. Environmental Protection Agency’s website for a list of laboratories that can test for cyanobacteria and cyanotoxins.

Can cyanobacterial blooms be treated?

There are no effective means of treating a cyanobacterial bloom once it appears. Treatment with algicides is not recommended as these compounds can cause the cyanobacteria to rupture, releasing any toxins contained within the cells. 

Several factors can contribute to growth of algal blooms, such as warm temperatures, low flow and the input of nutrients, such as nitrogen and phosphorus, into the water. Decreasing nutrient inputs into a waterbody is a strategy to help prevent blooms. Fertilizer runoff, animal waste, leaking septic systems and other point and non-point sources can add nutrients into a system.