Cyanobacteria (Blue-Green Algae) in Waterways

What Are They?

Cyanobacteria, often called blue-green algae, are common primitive microorganisms that can resemble algae but are uniquely classified with bacteria. Cyanobacteria are microscopic organisms that use sunlight to photosynthesize and produce their own food but lack a cell nucleus or membrane bound organelles like true algae. "Cyan" means blue, and cyanobacteria get their name from the blueish pigment phycocyanin. They also contain chlorophyll a similar to plants and use both pigments to capture light for photosynthesis (Crayton, 2004). Cyanobacteria occur naturally worldwide and can be found in oceans, ponds, lakes, streams and moist soil.

What Causes a Cyanobacteria (Blue-Green Algae) “Bloom”?

Cyanobacteria are a normal part of a healthy aquatic environment, but the population can "explode" in response to certain environmental conditions. High concentrations of cyanobacteria can form "blooms" within just a few days. There are three main factors that have shown to increase the likelihood of a cyanobacteria bloom in a body of water. First, since cyanobacteria are photosynthetic, they need direct access to sunlight for significant growth. More light in the spring and summer and corresponding warmer water temperatures have been associated with increased growth. Second, nutrient enrichment particularly nitrogen and phosphorous is essential for a bloom in waters with a pH range of 6–9. Cyanobacteria can bloom with phosphorous levels as low as 0.03 ppm (the New Jersey water quality standard is 0.05 ppm). Lastly, poor water circulation can facilitate growth of cyanobacteria. With mild winds or currents, large cyanobacteria colonies will accumulate on the leeward shore and expand rapidly as water becomes stagnant. Under these conditions a body of water can become very turbid with green, blue-green or a reddish-brown color, the appearance of a thin oily looking film resembling paint, or a thick floating scum on the surface. Three genera of cyanobacteria account for the vast majority of blooms: Microcystis, Dolichospermum (formerly Anabaena) and Aphanizomenon. A bloom can consist of one or a mix of two or more genera of cyanobacteria.

Cyanobacteria cannot maintain this abnormally high bloom population for long and will rapidly die and disappear after one or two weeks. However, if conditions remain favorable, another bloom can quickly replace the previous one. Successive blooms may overlap so that it appears as if one continuous bloom occurs for up to several months.

As long as nutrients remain in excess, cyanobacteria can grow until some other factor such as light or temperature limits their growth (fall and winter). Increased nutrients enter the water body as runoff from either point or nonpoint sources. Nutrient sources can include stormwater and agricultural runoff, runoff from fertilized lawns or recreation fields, sediments from soil erosion, improperly functioning septic systems, as well as from natural sources such as leaves, plant residues and woody material.

Impacts of Cyanobacteria

Some of the negative impacts of a cyanobacteria bloom include:

1. Spoiling water quality, producing odors or scum.
2. Making recreational areas unpleasant or unusable.
3. Dense blooms can block sunlight, which can kill other plants or animals in the water.
4. When not photosynthesizing to produce oxygen cyanobacteria still need to respire. This, along with decomposition from large bloom die-offs, uses large amounts of oxygen and can negatively lower the balance in the ecosystem to the point of causing fish "kills."
5. They can release potential toxins harmful to humans, pets and livestock.

Potential Toxins Associated with Cyanobacteria

Some, but not all cyanobacteria can produce toxins. Even blooms that contain known toxin producing species may not produce toxins at detectable levels. It is not known what triggers toxin production in the cyanobacteria. Toxins are produced inside the cells and stay there as long as the cells are alive. When the cyanobacteria cells die and break down, the toxins are released into the water. Toxin concentrations may vary dramatically and are not evenly distributed. Potential toxins include nerve toxins (anatoxins), liver toxins called microcystins, and dermatoxins (effect skin). It is not possible to tell if the cyanobacteria present in the water body are producing toxins without laboratory tests. These toxins have been known to kill livestock, dogs and wildlife that drink infested waters. Because of this, waters that show signs of cyanobacteria should be treated with caution.

While rare, humans that come in contact cyanobacteria toxins may result in health problems that include:

1. Skin rashes, hives and blisters.
2. Irritation of the eyes, nose and throat.
3. Possible breathing problems.
4. Abdominal pain, diarrhea and vomiting.

To protect yourself and your pets:

1. Don't swallow water from any waterway.
2. Don't swim or wade into areas that might have evidence of cyanobacteria.
3. If you swim in or come in contact with water that might have a bloom, wash thoroughly with fresh water as soon as possible.
4. Don't let pets or livestock drink, or enter water where cyanobacteria are present
5. If pets or livestock enter the water, rinse them off immediately. Do not let them lick the water off their fur.
6. Don't irrigate lawns with water that looks scummy or smells bad.

If symptoms from contact develop, contact your physician or veterinarian.

NJDEP Recreational Advisory Guidance Levels

The New Jersey Department of Environmental Protection (NJDEP) has developed a color-coded alert signage system that provides use recommendations for impacted water bodies based on levels of cyanobacteria and/or cyanotoxins present. More information or downloadable signage is available on the NJDEP website.

Prevention/Control of Cyanobacteria

While there are some short-term treatment options for controlling cyanobacteria, the long-term solution involves finding ways to reduce phosphorous and nitrogen inputs at their source, before they can runoff into a water body. Since nutrients come from a variety of sources, it is often difficult to pinpoint an exact cause.

Some management practices include:

1. Reduce excessive application of fertilizer on lawns; use soil tests to determine fertilization needs.
2. Grow lawn species that require less input of nitrogen and phosphorus fertilizers such as fine fescues or turf type tall fescue cultivars that have been shown to grow under low input of fertilizer and water.
3. Properly maintain septic tanks and fields.
4. Clean up pet waste and isolate livestock from water bodies.
5. Establish natural planting buffers adjacent to the water body. Rather than mowing to the edge, create a buffer strip of tall grasses and native plants, and maintain vegetation along the waters banks to filter runoff and prevent soil erosion.
6. As tree leaves and grass clippings break down, they are a source of nitrogen and phosphorous. Though beneficial if mulched into turf or composted and incorporated into soil, leaves and grass clippings should be raked from the water's edge and from curbs & gutters to prevent them from being washed into waterways.
7. Keep trees or establish new trees along the water's edge to help shade and cool surface water.
8. Reduce the amount of area in pavement or other impervious surface to control runoff directly into a water body.

If source control does not manage the cyanobacteria blooms, there are other options.

Copper based and peroxide algaecides will kill cyanobacteria but must be used early before the population gets too large. Most chemicals cause the cells to break up and release toxins all at once into the water. Killing a large population of cyanobacteria may result in a fish kill.

Phosphorous, a main food source, can be inactivated or "bound up" using chemical additives, such as buffered alum (aluminum sulfate combined with sodium aluminate at a ratio of 2:1). Alum can be applied to the water forming a precipitate "flock" that removes phosphorous from the water column as it settles. In addition, as alum covers the bottom sediments, it binds with, and reduces or prevents, the release of phosphorous from the sediment so this nutrient is not readily available to the cyanobacteria. Caution must be used when treating with additives as some can raise or lower the pH level. When the pH level falls below 6.0 or rises above 8.5, it may result in some additives becoming toxic and trigger a fish kill. Newer lanthanum-based products, such as Phoslock and EutroSORB, can bind phosphorous with little or no change in pH and may be a better treatment choice for some waterbodies. Due to the potential water quality changes, and to calculate the correct amount of additive necessary, it would be prudent for the lake owner to consult with a professional lake management specialist if considering using a phosphorous inactivation additive. More information can be found in Holdren et. al., (2001). It must be noted that phosphorous inactivation only treats the phosphorous that is currently in the lake or pond. Stormwater runoff can add new amounts of phosphorous to a pond and trigger new blooms.

Liquid dyes can be used to inhibit algal growth by reducing the amount of sunlight that reaches the bacteria. These easy to apply dyes tint the water blue or black and absorb the light waves used in photosynthesis. Dyes are most effective in lakes or ponds with a low flow to prevent the dye from washing out quickly. Dyes are popular for golf course ponds.

Underwater aeration promotes artificial circulation between the surface and bottom layers of the water body bringing oxygen poor water up to the surface. This can be achieved by using a small compressor, weighted airlines and one or more air diffusers, to introduce a plume of bubbles at the bottom of the water body. The rising air bubbles set up a circulation pattern within the water body that breaks down thermal stratification, horizontal water layers that form due to temperatures effect on water density; colder, denser water at the bottom and warmer less dense water at the surface. If the waterbody stratifies, the bottom layer will not get oxygen from the surface and can develop into an anoxic (very little oxygen) layer overlying the bottom sediments. If this happens, a chemical reaction occurs that results in the release of phosphorous into the water column where it can fuel additional bacteria or algal growth. Aeration more evenly mixes temperature, oxygen and nutrients throughout the water column. By increasing the dissolved oxygen content throughout the water column including the deeper waters at the bottom, more phosphorous should remain bound in the sediment.

The circulation also keeps cyanobacteria moving through the water so they can't maintain their optimum position in the water column. This helps to prevent them from reaching nuisance levels.

Barley straw bales are sometimes used in an attempt to control algae but have had mixed results in the control of cyanobacteria blooms (Mangiafico and Haberland, 2011). Barley straw does not kill existing algae / cyanobacteria but may act to prevent additional growth. The exact mechanism is not known but it appears to involve chemicals released as the barley straw breaks down over 2 to 8 weeks.

References and Additional Reading

1. The New Jersey Department of Environmental Protection. Division of Water Monitoring, Standards & Pesticide Control - Harmful Algal Blooms (HAB)
2. Crayton, M. A. 2004. "Toxic Cyanobacteria Blooms." A Field/Laboratory Guide. Office of Environmental Health Assessments Washington, Department of Health, Olympia, Washington.
3. EPA - Control Measures for Cyanobacterial HABs in Surface Water. Updated 2/26/24.
4. Holdren, C., W. Jones, and J. Taggert. (2001). Managing Lakes and Reservoirs. North American Lake Management Society and Terrene Institute and U.S. Environmental Protection Agency, Madison, WI. 382p.
5. Lembi, C.A. 2003. Factsheet on Toxic Blue-green Algae (PDF). Department of Botany and Plant Pathology, Purdue University. Revised 2012.
6. Mangiafico, S. and M. Haberland. (2011). Pond and Lake Management Part VI: Using Barley Straw to Control Algae. Rutgers Cooperative Extension Fact Sheet, FS1171, New Brunswick, NJ.
7. Moore, Brenda. 2009. Addressing Blue Green Algae Problems (PDF). Mona Lake Watershed Council. Muskegon, Michigan.
8. NOAA Center of Excellence for Great Lakes and Human Health (2009). Harmful Algal Blooms in the Great Lakes: What they are and how they can affect your health.
9. NOAA. Harmful Algal Blooms and Muck: What's the Difference?
10. Obropta, C.C. and E. Althouse. 2008. Pond and Lake Management Part 1: Dealing with Aquatic Plants and Algal Blooms. Rutgers Cooperative Extension Fact Sheet, FS1076. New Brunswick, NJ.
11. Van der Merwe, D, C. Blocksome, and L. Hollis. 2012. Identification and Management of Blue-green Algae in Farm Ponds (PDF). MF3065. Kansas State University Agricultural Experiment Station and Cooperative Extension Service.

February 2025