Harmful Algal Bloom FAQ

Algal Bloom News
Useful Links
  • Visit the Ohio EPA’s webpage for more general information about algae and HABs.
  • The City of Toledo has established a water quality dashboard to provide citizens with the latest water quality status water from the City’s treatment plant. Visit Toledo’s dashboard.
  • Ohio EPA’s Public Water System Harmful Algal Bloom Response Strategy provides guidelines on monitoring and sampling protocols, identifies acceptable analytical methods, identifies cyanotoxin levels that will be used to make drinking water use advisory decisions, and recommends contingency planning for public water systems.
  • NOAA hosts recent satellite imagery of Lake Erie from the MODIS equipment onboard NASA’s Aqua and Terra satellites. Algal blooms are often easily visible in the imagery. View the latest satellite images.
  • The City of Toledo maintains a buoy to monitor conditions near the water intake for the Collins Park Water Treatment Plant. Visit the buoy’s reporting site.


In August 2014, there was an algal bloom in western Lake Erie that resulted in the City of Toledo issuing a notice to Toledo water customers not to use their water. The water ban lasted for just over 2 days.

Visit the NASA Earth Observatory site to view images of the HAB on western Late Erie in August 2014.

Credit for Images: NASA Earth Observatory, August 2014;

What Causes Blooms to Form?

Like plants and true algae, cyanobacteria have a pigment called chlorophyll that captures sunlight to photosynthesize sugars for energy. Aquatic plants and algae require nutrients, especially phosphorus and nitrogen, from the water or sediment to grow. Not all algal blooms are HABs. Some true algae-like Cladophora can also create large blooms with the right nutrient and light conditions. Such blooms can be a serious nuisance and cause environmental problems but do not generate the toxins associated with many cyanobacteria.

Factors that can contribute to HABs:

  • Excess nutrients (phosphorus and nitrogen)
  • Sunlight
  • Low-water or low-flow conditions
  • Calm water (low wind conditions)
  • Warmer temperatures
  • Low salinity
  • Selective grazing (avoiding cyanobacteria) by zooplankton or zebra/quagga mussels

The presence of cyanobacteria does not necessarily mean that toxins are being produced. The level of toxicity depends on the strains present and environmental factors. HAB toxicity also depends on the sensitivity, age, and sex of the animal or person that consumes or comes into contact with the toxin.

What is a Harmful Algal Bloom?

A harmful algal bloom (HAB) is a large growth of planktonic bacteria. HABs are actually cyanobacteria, which are commonly referred to as “blue-green algae” and may produce toxins. These toxins may affect the liver, nervous system and/or skin.