Water in My Outdoor Fountain Keeps Turning Green

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A classic, tiered fountain provides an elegant focal point in a garden.

Take the steps to prevent algae in your outdoor fountain to ensure that you have a relaxing water feature and not something that looks like a slimy green Halloween prop. Regular cleaning and maintenance will keep both algae and calcium deposits from accumulating.



Algae that tints the water green is called green-water or pea soup algae, while algae that grows in long strands is called hair or string algae. Both types often plague outdoor fountains. Clean your outdoor fountain at least once per month. Use an old toothbrush, warm water and dish detergent to scrub the bowl, pump and any rocks. Use vinegar, mouthwash or lemon juice to clean the surface the algae is particularly stubborn. Refill your fountain with clean, clear water.

Natural Algae Controls

Algae, like any plant, needs water and sun to survive. Add water hyacinth or water lilies to block sunlight and compete with the algae for nutrients.


Natural microbial controls, available at many garden centers, introduce beneficial bacteria into your fountain. This beneficial bacteria feeds on nutrients and converts them to compounds which the algae will not use for food.

Chemical Algae Controls

If algae is a persistent problem, add a commercially-available algaecide or pond clarifier to the water. Read the label closely to ensure that any product you add is safe for birds, pets and plants. Fountec and GreenClean are two enviromentally-safe algaecides.


Sometimes chemical algae controls work too well and kill off all of the algae at once. When this happens, a new crop of algae will feed off of the dead organic matter The cycle then begins again. Prevent this by cleaning the fountain before applying algaecide.



Bethany Wieman

Based in the Midwest, Bethany Wieman has been writing articles about gardening, DIY, finance, travel and sustainability for more than 10 years. She was featured in the book "The Complete Guide to Growing Vegetables, Flowers, and Herbs from Containers." Wieman's professional background is in marketing, working with such brands as Swiss Army, Timberland and Callaway Golf. She holds a Bachelor of Arts in English.