Phytoplankton and Cyanobacteria


Phytoplankton are a key indicator of overall lake heath and biodiversity. A strong link has been found between the level of phosphorous and the amount of dangerous cyanobacteria, also known as blue-green algae, which are microorganisms with the ability to photosynthesize, making them closer in relation to bacteria than plant life. Blue-green algae most commonly appears in the form of a “bloom,” or a highly concentrated population that can appear over a few days. An algae bloom typically lasts no longer than two weeks, but the rapid regeneration of algae blooms in the same area can create the illusion of a single bloom lasting for several months (Hershener, C. & Havens, K.J. 2008). These blooms are hazardous to humans not because they themselves are toxic, but because they create toxins. Not all strains of blue-green algae produce toxins, but it is difficult to predict because a single bloom might have many strains that do contain toxins, and many others that do not. Overall, most blooms are not toxic, but since it is difficult to tell, psrevention of these blooms is thus the best way to prevent human exposure to these toxins (Hershener, C. & Havens, K.J. 2008).

Short term side effects of cyanobacteria, when exposure is limited to swimming or physical interaction include nausea, diarrhea, stomach pain and skin rashes. Long term effects of cyanobacteria exposure, such as drinking contaminated water or any internal exposure, might rarely include nerve and liver damage. Globally, there are no confirmed deaths by exposure to cyanobacteria, but pets and animals have died from exposure (State of Washington dept. of ecology 2010).

Spreading liquid manure on a farm field near St. Albans Bay in Vermont

Cyanobacteria problem areas in Lake Champlain are Missisquoi Bay and St. Albans Bay. These are calmer areas of the lake, which allows the blue-green algae to accumulate in thick layers by the shoreline. The source of 50% of the non-point nutrients that run off into the lake come from these two bays.

Management attempts are varied, both in method and rate of success. The key to reducing cyanobacteria blooms is to reduce the amount of phosphorous and nitrogen in the water, which can be difficult in Vermont. The main sources of excess phosphorous and nitrogen come from fertilizer runoff, from both grass and agriculture. Municipal and residential runoff also contribute (VT Dept of Health, blue-green algae. 2005). Currently, there is no way to remove excess nutrients when they have been added to the water, so the best method is prevention and reduction of runoff.

In the Saginaw Bay portion of Lake Huron, an invasion of zebra mussels initially cleared the waters of excess nutrients and lowered the overall concentration of cyanobacteria, blue-green algae blooms in particular. The methods for removing blue-green algae blooms prior to this invasion included physically removing the algae blooms from the water, which did do anything to alter the nutrient content of the water, and increased recycling of phosphorous throughout the hotter summer months. However, three years after the invasion, the amount and frequency of blue-green algae blooms returned to pre-invasion levels (Hershener, C. & Havens, K.J. 2008).


Hershener, C. & Havens, K.J. (2008). Managing Invasive Aquatic Plants in a Changing System: Strategic Consideration of Ecosystem Services. Conservation Biology, 22(3), 7. Retrieved from

Lake champlain land trust, blue-green algae on lake . (n.d.). Retrieved from

State of Washington dept. of ecology, algae control program. (2010). Retrieved from

VT Dept of Health, blue-green algae. (2005). Retrieved from


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