Pond Algae 101 - Why Is My Pond Green?

Ponds often become challenged by pond algae, pond scum, and other aquatic plant growth. This can be unsightly, produce an unpleasant pond odor, cause fish kills, and provide fertile breeding grounds for mosquitoes. Why does this happen?

The root causes of this pond algae are the excess nutrients, such as nitrogen and phosphorous. These come from a number of sources such as: 1) fertilizers from yards, farms, and golf courses; 2) leaves, grass, and other organic debris; and 3) waterfowl or animal excrement. The majority of these elements enter the pond via stormwater runoff from houses, streets, or other impervious surfaces (meaning they don't allow water to be absorbed). These nutrients then fuel aquatic plant overgrowth, and in doing so suck the oxygen out of the pond, essentially killing the pond's ecosystem.



The diagram above portrays the problematic cycle that can be created by excess nutrients flowing into pond and lake ecosystems. Small outbreaks of pond algae can quickly turn into surface-covering algae blooms that will deplete the oxygen supply and begin to harm the pond ecosystem. If the process is allowed to continue unabated, pond eutrophication can occur.

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