How to Effectively Control Algae Growth in Ponds

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How to Effectively Control Algae Growth in Ponds

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A common occurrence in many ponds across most of the United States during the summer months is the growth of algae. Algae growth gives water bodies a green appearance which, when closely examined turns out to be mats of plants floating on the surface of the water. Often referred to as ‘scum’, the growth of algae in ponds is unacceptable to most people.This group of plants is a mystery and poorly understood by many. So, let’s unravel the mystery behind algae and point out why their growth in ponds must be effectively controlled.

What are algae?

Algae is a term used for a large group of photosynthetic plants that can form colonies or mats on the surface of a body of water.  Algae plants do not have true roots, stems, leaves, vascular tissue, but have simple reproductive structures. They are distributed worldwide in the sea, in freshwater and in wastewater. Most algae are microscopic, but some are quite large, e.g. some marine seaweeds. There are as many as one million species of algae which are generally classified as either good algae or bad algae.
  • Good algaemake up the majority of algae species and are often referred to as green algae and diatoms. Good algaeserve as a foundation food source for numerous aquatic organisms. In addition, good algae can be cultivated for the production of a wide range of commercially interesting byproducts such as fats, oils, sugars, and functional bioactive compounds.
  • Bad algae are fewer and referred to as cyanobacteria, blue-green algae (BGA), or harmful algal blooms (HAB). Bad algae do not serve as a food source for aquatic organisms. Furthermore, bad algae can:
  • Be toxic and cause serious illness in humans, pets, and livestock.
  • Make water not safe to drink and expensive to treat.
  • Create dead zones by depleting water of its natural oxygen. This lack of oxygen can lead to the development ofdead zones, or areas where aquatic plants and animals cannot survive.

What factors contribute toalgae growth in ponds?

Despite there being more good algae species, it is bad algae species that are of concern.A characteristic of bad algae (BGA or HAB) is the occurrence of algal blooms. Algal blooms:
  • Occur when algae cells clump together to form surface scum which appears on top of the water like chopped grass blades, or as thin blue/green mats, or as green paint spilled.
  • Typically occur in the summer months when there is a lot of light, long days, warm days, and stagnant conditions.
  • Outbreaks reported to have increased by 18 percent between 2018 and 2019.

What contributes to the occurrence of algal blooms?

  • Pollution
    • BGA/HAB are more prevalent when there is excessive amounts of phosphorus and nitrogen. When phosphorus and nitrogen fertilizers are applied in excess, these nutrients can enter water bodies via chemical runoff or soil erosion.
    • Poor sewage management also introduces phosphorus and nitrogen into surface water systems.
  • Light Exposure and Water Movement
    • Algae are photosynthesizing organisms and require the right amount of light to thrive.
    • Good algae which thrive best in clear waters that are shallow. In contrast, BGA/HAB have the ability to move throughout the pond and adapt to variable conditions.
  • Turbidity and Temperature
    • Turbidity is a measure of how clear or cloudy a body of water is and impacts light exposure and temperature of the water.The more turbid the water, the warmer the water will be, allowing the algae to grow faster.
    • As algae blooms continue to grow and water becomes increasingly turbid, BGA and HAB thrive.
  • Climate change
    • Climate change is expected to have many effects on freshwater ecosystems.
    • Climate change combined with increased stormwater runoff packed with nutrients can result in conditions favorable for algal blooms.
    • With a changing climate, HABs can occur more often in freshwater bodies and may become more intense.

How to control algal blooms in ponds.

There are three methods used to manage algae: physical/mechanical,biological, and chemical.
  1. Physical/mechanical method – which raking or dredging, mowing, and harvesting the algae.
    • Highly effective on a small scale. However, for large ponds, physical removal of algae blooms requires expensive harvesting equipment.
    • To be an effective method of control, the algaeneed to be taken out of the water and disposed of where nutrients and fragments cannot re-enter the pond or lake.
    • It may be necessary to repeat physical removal during the growing season.
  2. Biological method–involves introducing plants or animals that compete with or feed on algae.
    • Some type of carp fish will feed on mat forming algae when their food source is depleted.
    • The use of carp to control algae is variable and will limit the potential to use copper-based algaecides.
  3. Chemical method –involves the application of algaecides. For example:
    • Copper salts and chelated copper compounds.
  1. Copper sulfate – anold andinexpensive standby that disrupts cell membranes in algae. However, copper sulfate is:
    1. Less effective in hard water (which has high calcium and magnesium content),
    2. Toxic to fish at low pH, and
    3. Most effective when water temperatures are above 60 F.
  2. Chelated copper compounds– disruptcell membranes in algae and are relatively expensive. Chelated copper compounds:
    1. Can prevent copper from precipitating out of solution in hard water, and
    2. Are most effective when water temperatures are above 60 F.
    • Oxidants and hydrogen peroxide
  1. Can be as effective on algae as copper but are much less effective on algae species that are more difficult to control,
  2. They disrupt cell membranes and walls, and
  • Work best where water pH range is 6.8 to 7.8, and at all temperatures.
    • Dye materials
  1. Are more expensive than copper sulfate but less than chelated copper,
  2. Work by blocking portions of the light spectrum necessary for photosynthesis,
  • They should be used early in the season before algae has extensive growth, and
  1. May not work well in waters that are less than 2 to 3 feet deep.
Enhancing the control of algaein ponds
  • Surfactants with d-limonene as the active ingredient, e.g., Cide-Kick® and Cide-Kick II®, or similar surfactant, can be added to an algaecide for enhanced control of floating mats or difficult to control species of algae.
  • For best results, follow all instructions on algaecide and adjuvant product labels for application rates and use directions.

Additional reading

  • Preventing Algae Blooms from Taking Over Ponds and Lakes
  • Use Cide Kick Nonionic Surfactant in Control of Invasive Aquatic Plant Species
  • Cide-Kick II for Excellent Management of Weedy and Invasive Plants


Camberato, D.M. and R.G. Lopez. 2010. Controlling Algae in Irrigation Ponds. Purdue University Extension Service publication HO-247-W. [Verified April27, 2022]. Environmental Resilience Institute, Indiana University. 2021. Climate Implications – Harmful Algal Blooms. [Verified April 27, 2022]. Environmental Working Group. 2019. Algae Outbreaks Up by Nearly One-Fifth in 2019. [Verified April 27, 2022]. Guiry, M.D. 2012. How many species of algae are there? Journal of Phycology 48: 1057-1063. DOI: DOI: 10.1111/j.1529-8817.2012.01222.x.,  [Verified April 27, 2022]. National Institute of Environmental Health Sciences. 2021. Algal Blooms. [Verified April 27, 2022]

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