What is a harmful algal bloom?

A harmful algal bloom (HAB) is a dense concentration of cyanobacteria (also known as blue-green algae) in the water that can be considered harmful due to toxins and aesthetic, economic, or ecological impacts. HABs are typically identified by a dense film of floating algae on the surface of the water.

Some species of cyanobacteria produce toxins under some conditions. However, it remains unclear to scientific experts when and why the cyanobacteria produce these toxins. As a result, any given HAB may or may not cause toxins to be in the water. The toxins span a wide range of chemicals, including liver toxins, nerve toxins, and skin irritants. More information on the toxins can be found on the CDC website.

The NYS DEC has three categories for HABs: 

  • Suspicious Bloom – Visual observation of an algal bloom by a trained observer
  • Confirmed Bloom – Cyanobacteria concentration exceeds 25 ug/L
  • Confirmed Bloom with High Toxins– Cyanobacteria concentration exceeds 25 ug/L and a concentration of toxins above a given threshold

You can learn much more about HABs at the NYS DEC website.

The Jefferson Project's Response

What was observed?