Harmful algal blooms have been a big issue in the Finger Lakes over the past several years. In 2017, all eleven of the Finger Lakes appeared on the NYS DEC Harmful Algal Bloom notification page. In freshwater, Harmful Algal Blooms are generally caused by cynobacteria, which are commonly referred to as blue-green algae.

Cyanobacteria are a group of bacteria that rely on photosynthesis for their energy. They are often confused with algae even though they are unrelated to algae. Cyanobacteria are common organisms that are always present in ponds and lakes. Many types of cyanobacteria are able to fix atmospheric nitrogen, so they have an advantage over other aquatic microflora when nitrogen is the limiting nutrient. In situations where phosphorous levels are high, nitrogen is usually limiting and populations of cyanobacteria can take off, causing a bloom. A phosphorous/ nitrogen imbalance is the most common cause of a cyanobacterial bloom, but there are other situations that can cause blooms that are poorly understood.

Some types of cyanobacteria can produce toxins, the most commonly detected of these is called microcystin. Microcystin and other toxins caused by cyanobacteria can cause diarrhea, nausea or vomiting, skin, eye or throat irritation, allergic reactions or breathing difficulties they are also known to cause liver damage. It is difficult to determine if a cyanobacterial bloom contains harmful toxins, so if you see water that might have a bloom, it is best to avoid it. If you come in contact with what you think may be a harmful algal bloom you should first rinse thoroughly with clean water and stop using the suspected water. You should seek medical attention if any symptoms develop. Pets should be kept away from harmful algal blooms. If you think you see a harmful algal bloom, report it to the NYS D.E.C.

Cyanobacteria are often confused with green algae. Cyanobacteria can give water a spilled paint appearance, a pea soup appearance, green streaks on the water, or floating dots or clumps. Green algae can form into large, floating mats on the surface of a lake or pond, they can also look like bubbling scum on the water. Green algae can have an unpleasant smell and can look gross, but does not produce harmful toxins.

Because cyanobacteria are nitrogen fixers, they can take advantage of high phosphorous levels and often bloom when there is too much phosphorous in a body of water. Blooms also are more likely to occur in warmer waters. Wind mixes the water which can disrupt the life cycle of cyanobactria, so calm weather also increases the probability of cyanobactrial blooms. Since we have little control over the weather, the best way to reduce the probability of a cyanbacterial bloom is to limit phosphorous levels and, to a more limited degree, nitrogen levels. If you have a pond on your property, you can limit nutrient inputs by limiting lawn fertilization, maintaining septic tanks and shoreline buffers, reducing erosion and stormwater runoff, and maintaining water movement. These steps can also reduce nutrient runoff into lakes where cyanobacteria could be an issue.

For more information about harmful algal blooms, visit the New York State DEC harmful algal blooms website:

Last updated November 20, 2017