Filamentous Algae Control: 4 Ways to Kill Filamentous Algae

Algae Control Aquatic Weed Control Filamentous Algae Inert Dye Lake Rake Natural Bacteria



4 Ways to Get Rid Of Your Algae


The most common lake weed problem is Filamentous Algae.  Filamentous Algae, also called “lake moss” or “pond scum”, form dense mats of strands.  Filamentous Algae is often a persistent problem because it reproduces rapidly by fragments, spores and cell division.  Abundance is dependent on nutrient levels, particularly phosphorous, in the water.  High levels of nutrients result in increased amounts of algae. 

Its presence can degrade water quality and recreational enjoyment.  Excessive algae can cause oxygen depletion when it decomposes, as a result of natural die-off or an algaecide application.  This is often the cause of a fish kill, depending on how low oxygen levels get. 


4 Control Methods are:

1.  Mechanical Control

Pond algae removal can be accomplished by physically lifting large floating clumps with a rake. Mechanical removal is an ongoing activity during the growing season due to the persistent fast growth.  Pond algae removal will result in large piles that can be reused for composting or garden mulch.

2.  Biological Control

  1. One method of biological control is to fertilize your pond to encourage the development of planktonic algae that will reduce water clarity.  Reduced clarity means less sunlight reaching the pond bottom, which in turn reduces growth of filamentous algae. 
  2. Another method of biological control is to reduce watershed or outside sources of nutrients.  Algae get their nutrients from the water, so minimizing nutrient levels is a worthwhile management activity.  Common sources of unwanted nutrients are Canadian geese, lawn fertilizer, domesticated animals, agricultural fertilizer, and even septic systems if located too close to a pond.  Pond muck can be reduced with a natural bacteriaapplied weekly.

3.  Chemical Control

a) Selecting a chemical to control Filamentous Algae is situation-specific and the pond owner needs to consider several factors. For a list of optional control methods call Aquacide Company 800-328-9350.

b) Applying the correct amount of chemical is crucial to successfully controlling algae.  All product labels provide dosage or application rates, often as pounds or gallons per acre-foot of water.  To confirm application rate call us directly.

c)Timing of chemical applications is another important consideration.  Some algae species can reach nuisance levels in cold water just after ice-out.  However, many work best in water warmer than 60 degrees F, and use in colder water will yield less than desired results.

4.  Inert Dyes

Inert dyes can be used to control Filamentous Algae.  The color they turn the water, usually blue, reduces sunlight penetration, which in turn reduces growth of algae.  These dyes are not effective in water less than 2 feet deep.  Inert dyes are not recommended for use in ponds with considerable water exchange during a rain. 


Read what our customers have to say about our products:

Review for Cutrine-Plus Liquid

“Sprayed on Saturday with Cutrine-Plus/Cygnet Plus cocktail…I drove by the pond on Sunday and already the algae was nearly gone.  Wow!!!”

J.D., Fredericksburg VA


Next Steps:

To visit our online here

To Request our product catalog click here

To learn about lake weed analysis click here


For complete article see: "Controlling Filamentous Algae in Ponds," William E Lynch Jr. Ohio State University

Filamentous Algae, Wikipedia – free encyclopedia

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  • Tom Markoe on

    Hi Jay,
    Most likely it is filamentous algae. Ponds typically turn over once in the spring and once in the fall so that is probably about the time the pond turned over that you had all the dead floating algae. Feel free to send a physical sample to the address below for confirmation.

    You could also look into the AquaClear Blog

    Thank you,

  • jay clinton on

    after a freeze over my 3/4 acre pond has a green like moss substance on it when it thawed

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