Cyanobacteria (also known as blue-green algae) are aquatic photosynthetic bacteria that are naturally occurring in most if not all freshwater systems.

Cyanobacteria require nitrogen and phosphorus to grow and replicate. When nitrogen and phosphorous levels in a waterbody are elevated,  cyanobacteria can replicate profusely and create a bloom. These blooms usually cause the water to appear green and can create scums on the water’s surface and on the shoreline.

In addition to the unsightly and often foul-smelling green slime observed during a bloom, cyanobacteria is a cause for concern because many species produce harmful toxins. At high levels, these toxins can cause health risks for humans and animals such as skin rashes, digestion issues, and/or liver and nervous system damage. These health risks are increased for young children and pets. Though cyanobacteria are being heavily researched, there are still many unknowns, especially related to long-term health effects.

Due to the health risks, it is important to be aware and cautious of cyanobacteria and refrain from touching it, swimming in it, and especially ingesting it.

The following table, produced by the US Environmental Protection Agency, outlines the probability of health effects based on the number of cyanobacteria present in a water sample:

Cyano Levels

State and town programs for testing waterbodies for cyanobacteria are often lacking and beach closures and announcements of blooms are often delayed. Even if a public beach is open, that does not necessarily mean the water is safe.

For more information about cyanobacteria and cyanotoxins, please visit the Environmental Protection Agency website.

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