Waterscapes 101

Harmful Algal Blooms 

What is cyanobacteria or harmful algal bloom?

Cyanobacteria, is commonly referred to as blue-green algae or harmful algal bloom. Cyanobacteria can be confused with algae because of the coloration. A visual inspection of a "bloom" will not reveal whether it is cyanobacteria versus algae.

Cyanobacteria blooms often occur in warm, calm water where nutrient levels are high. Heavy nutrient sources include uncontrolled sewage discharge, agricultural run-off, and fertilization of adjacent grass areas.


There are many species of cyanobacteria. Based on the species, the visible cyanobacteria characteristics vary. Planktothrix forms a green pollen-like film covering the surface. Mycrosystis and Dolichospermum form green paint-like slick on the water surface and near shorelines. As the surface films age they can appear to be bubbling and may take on different coloration. Other cyanobacteria species are found below the surface of the water making detection difficult. In order to confirm that a bloom is cyanobacteria, it must be tested. You cannot reach a conclusion based on appearance alone.

Important facts about Cyanobacteria

Exposure to cyanotoxins released by Blue-green algae can have extremely serious health impacts for humans, domestic animals, wildlife, and aquatic life.

The release of toxins occurs during the death or rupture of cyanobacteria cells. These toxins include endotoxins, neurotoxins, and hepatoxins. Exposure to cyanotoxins can occur from swimming in infested areas, ingestion of contaminated water, and breathing in toxins when near affected waters. It is important to note that even boiling water infected with cyanobacteria will not kill the toxins.

Effects of exposure include skin irritation(endotoxin), abdominal pain(endotoxin), headache(endotoxin), vomiting(endotoxin), diarrhea(endotoxin), respiratory disease(neurotoxin), paralysis (neurotoxin), liver failure(hepatoxin)and even death.


Prevention is the best approach

Nutrient reduction is important for controlling of cyanobacteria. It is important to determine the source of excess nutrients.

Run-off? Sewage? Fertilization? For known sources- find ways to reduce inputs like diverting flow from runoff, planting vegetation to create a buffer, limit amount of lawn fertilizing. Other sources include organic muck accumulation from dead leaves and vegetation, fish and waterfowl waste.

Although total nitrogen, and total phosphorus elevations are key factors in cyano blooms, simply the presence of these nutrients in water does not result in a bloom. Studies have shown that cyanobacteria blooms occur more frequently when the N:P ratio drops below 29:1.(Science 221 (4611), 669-671)

Based on this research, if TP (total phosphorus) is lowered, then so is the likelihood of a blue-green algae bloom. Total phosphorus can be lowered safely by treating the water with a Phosphate binder such as Phosphate Eliminator. To limit new phosphorus from releasing from organic muck, bottom aeration should be used to increase oxygen levels.

Algaecides can be used to kill blooms in their early stages. There is the possibility for toxins to release from cyanobacteria after application. This is because the cyanotoxins release when the cells die.


Cyanobacteria and Pond Fertilizing

Water quality analysis should be completed before adding fertilizer to a trophy bass pond. Since the ratio of Total Nitrogen to Total Phosphorus is a key factor in the occurrence of cyanobacteria, adding too much Phosphorus can force the ratio into a range where a cyanobacteria bloom could occur. A small amount of Phosphorus will go a long way when fertilizing a pond. If you have any doubt about the correct amount, consult with a professional familiar with pond nutrients and nutrient ratios.

For help preventing cyanobacteria and high nutrient levels email us at support@naturalwaterscapes.com

harmful algal bloom
cyanobacteria characteristics

Treatments to Reduce the Risk of Harmful Algal Blooms