How to Eliminate Blue Green Algae


Nothing can be more disheartening on a hot summer day than finding a lake or stream ridden with ill-colored waters from blue-green algae. These cyanobacteria prosper in warm waters that are rich in nutrients and exposed to bright sunlight. Chemicals can be employed to kill the algae, but creating an aquatic environment that deters the growth of algae is the most responsible and often least expensive solution. Shading the water surface to lower water temperatures, reducing fertilizer run-off into lakes and streams and planting native vegetation can all reduce the amount of algae in water.

Step 1

Contact your local Department of Public Works, Natural Resources or other water-quality bureau to discuss your situation. Private ponds or public-access lakes can be affected by blue-green algae at similar times of year or may be caused by a common problem. These resources can best advise you of local conditions, governmental programs and ongoing work, and recommendations to rid the algae from your water body, too. Don't contact them if the issue is in a small ornamental water feature.

Step 2

Reduce run-off of phosphorus from the lawn, garden and home. Fertilizers that are over-applied or incorrectly scattered can leach quickly into storm sewers or erode down hillsides and shorelines into the water. Using clothing and dish detergents that are phosphorus-free also eliminates waste water that is high in nutrients that may be drained into local streams or lakes.

Step 3

Cool the water temperatures by shading the water surface. Planting native or non-invasive aquatic plants can shade the water, cooling it and reducing the amount of light available to the algae. Water lilies and native pond weeds also can provide food and habitat for fish and other wildlife.

Step 4

Amend situations of erosion. Planting hillsides or shorelines with vegetation reduces the quick flushing of pollutants and soil into waterways, potentially creating an environment more conducive for algae. Avoid planting designs that require fertilizers so that you are not increasing the amount of phosphorus at the edge of waterways. Choose low maintenance native plants.

Step 5

Investigate algacides, or chemicals specifically geared to the control of algae. Follow label directions carefully, as improper usage and dosages can cause more harm than good to both wildlife, desirable plants. Moreover, if living algae is killed too quickly or in mass amounts, the decaying algae releases nutrients into the water, potentially making it more favorable for the algae to prosper again. Decaying algae can also diminish the amount of oxygen in the water, harming fish.

Tips and Warnings

  • Do not bathe or drink water that is ridden with blue-green algae. Heavily infested water with often have a green, brown, yellow or maroon color, often with floating scum pads. Keep pets away from contaminated water, too. If skin irritations, eye soreness or vomiting occurs after swimming in or accidentally drinking infected water, contact your state Poison Control Center immediately.


  • Wisconsin Department of Natural Resources: FAQs on Blue-green Algae
  • "Your Garden Pond: Practical Tips on Planning, Design, Installation and Maintenance"; K. H. Wieser and P.V. Loiselle; 1996.
  • "The Pond Doctor: Planning and Maintaining Healthy Water Garden"; Helen Nash; 1994.

Who Can Help

  • New York State Department of Health: Blue-green Algae Information Sheet
Keywords: algae bloom, dirty water, lake algae

About this Author

James Burghardt has written for The Public Garden, Docent Educator, numerous non-profit newsletters and for's comprehensive plant database. He holds a Master's degree in Public Horticulture from the University of Delaware and studied horticulture and biology in Australia at Murdoch University and the University of Melbourne's Burnley College.