Pond Algae Causes Problems And Cures

Reviewing the questions we receive,  I find that there are still a lot of misunderstandings about the nature of filamentous pond algae. It is really pretty simple, but you have to take a serious look at cause and effect, and the differences between the types of algae present in pond and lake water.

Pond algae causes problems and cures

There is algae of a variety of types present in most untreated water. There is one cause for outbreaks of filamentous algae on the surface of ponds and lakes, and that is the penetration of sunlight to the lake bed. Filamentous algae in small quantities does no harm, and is usually limited to a small strip around the pond, and in some shallow areas. Pond algae becomes a problem when it takes over a large portion of a body of water. There are several problems related to excess pond scum.

Problems caused by excessive pond algae


Fish eat mosquitoes and mosquito larvae in large enough quantities to prevent them from becoming a serious problem in normal pond and lake situations. When filamentous algae and lake weeds become over abundant, the mosquitoes and their larvae are protected from the fish and can produce at near uncontrollable rates.


Pond algae, like any other plant, inhales carbon dioxide and exhales oxygen, but that is only part of the story. During the late afternoon in the summer, the opposite can occur, leaving fish to come to the surface to fight for air. When the algae dies and begins to rot, further dissolved oxygen depletion occurs.


Too much filamentous pond algae can make any aquatic recreational activity difficult.
-Aesthetics. Lake algae looks bad. It can also produce an unattractive odor. It’s just not something that most people want to be around.

The real pond algae problem

Most importantly though, pond scum is a symptom of another problem, and that problem is fertility. In some cases excessive algae growth occurs as a result of excessive fertility. In my experience, this is rare. When excessive fertility is involved, it usually results in an over abundance of plankton like, unattached single cells resembling a pea soup. In the vast majority of cases, the opposite is true. If there is not enough fertility present in the water, plankton, or algae bloom does not occur, and because the water lacks the sunlight filtering shading properties which phytoplankton provides, sunlight reaches the bottom, and a crop of filamentous algae results. This algae starts at the bottom, and gradually gains buoyancy and floats to the top under the influence of it’s own oxygen production. Blanket weed pond scum is the first noticeable indication that something is seriously wrong with a pond, and that something is the lack of phytoplankton.

Phytoplankton produces shading that prevents the sunlight from initiating the growth of  pond scum, but more importantly, it is the beginning of the food chain in your pond, and without a healthy algae bloom, your fish go hungry, and the life cycle is slowed or halted.

Solving pond algae problems

To prevent blanket weed, and to kick start the food chain, all that is needed is additional fertility. Test the pH of your water, amend it if needed, and start a regular fertility program. You will be amazed at the results. Your pond will be properly colored, and pond algae kept to a minimum, and your fish will be healthier.

To learn more about pond algae causes problems and cures see: The Lake Management section of this site, and How To Fertilize A Pond Or Lake.

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