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.