All About HABs

What is a harmful algal bloom (HAB)?

Although cyanobacteria are commonly referred to as harmful algae or blue-green algae, they are not really algae, they are bacteria. Under the right conditions, populations of cyanobacteria can grow quite rapidly forming what are known as harmful algal blooms (HABs). 

Cyanobacteria blooms (HABs) are likely to produce a range of natural chemical compounds, many of which are toxic to humans and pets. These toxins, termed cyanotoxins, can cause health concerns if touched, ingested, or inhaled. Likewise, the increasing presence of HABs on Cayuga Lake poses a risk to those who use the lake for drinking water and may hinder any recreation activities from occurring. HABs are not to be confused with excessive algal growth that is a common occurrence in freshwater lakes and ponds which can sometimes be referred to as an algal bloom. This excessive algal growth generally does have negative implications for the surrounding ecosystem, however it is not known to be toxic to humans.

How can you tell if a bloom is a HAB?

HABs have been described as having the appearance spilled green paint or pea soup. They can also look like parallel streaks in the water or like green dots. Non-toxic algae tends to look more like floating mats or hairy, as if  green tumbleweed was submerged in the water. Below are some examples to help identify toxic cyanobacteria blooms (HABs) using images from the DEC photo gallery.

Examples of HABs:

Examples of excessive growth of common algae:

What are the main causes of HABs?

According to a study conducted by the DEC, four factors were found to be correlated with HABs occurrences: phosphorus levels, presence of dreissenid mussels, maximum lake fetch length, and the lake compass orientation of its maximum length. For every 0.01 mg/L increase in Phosphorus levels, the probability that a body of water will produce a HAB increases by roughly 10-18%. However, the other three factors have a much greater range of uncertainty. The presence of dreissenid mussels are estimated to increase the probability of HABs by 18-66%, a northwest orientation of the longest fetch length is estimated to increase HABs probability by 10-56%, and finally, every mile of increased fetch lake is estimated to increase the probability of HABs by 20%. More information on this can be found in the Cayuga Lake HABs Action Plan here:

While these four factors were identified by the DEC, they are likely not the only four that exist. According to Rollwagen-Bollens et al. (2018), “Many different biotic and abiotic factors influence the dynamics of cyanobacterial blooms, often acting synergistically.” This likely contributes to the difficulty in predicting cyanobacteria bloom occurrences. As noted in the Cayuga Lake HABs Action Plan, some lakes that seem to have all of the factors that contribute to HABs development will not experience HABs, while there have been such blooms in lakes that have lower nutrient levels and likewise would not be predicted to have HABs. With further research and detailed datasets (like those produced from lake monitoring!) we can hopefully grow to better understand the factors that influence HABs in the near future.

What are the effects of HABs on Cayuga Lake?

 Toxins in harmful algal blooms can pose a threat to people and pets that have been exposed to them. Therefore, localized HABs prevent recreation activities from occurring where present on the lake until after they have dissipated. These toxins can also affect small fish and other freshwater animals, potentially harming the local aquatic wildlife. Likewise, HABs also have the potential to harm the local fishing scene and cause a decline in waterfront property value, hurting the local economy.

More details about the effects of HABs can be found the EPA’s website here.