By: admin | Posted On: October 18th, 2010 | 8 Comments | In: Uncategorized


The topic and problem of pond scum is an issue that at some time or another, likely affects all pond owners. The problem with trying to fix or even diagnose an issue of pond scum is that it is used as a very loose term and many people will refer to floating aquatic plants, weeds, or other floating material as pond scum. Pond scum is an actual term that refers to filamentous algae, but is often used to describe things other than pond scum; like some people I know!
So, what is pond scum? The technical definition is a filamentous algae that forms mats upon the water’s surface. These algae usually form on the bottom or sides of a pond and become buoyant and float to the water surface because of the oxygen bubbles it has produced. Once at the surface, pond scum can quickly cover the pond’s surface, giving the pond a dirty appearance. Remember pond scum is NOT floating plants like duck weed, water meal, or planktonic algae (green water).
Why does a pond get pond scum? Typically the formation of pond scum occurs from a high level of nutrient build up in the pond; mix that with higher water temperatures and longer daylight hours of summer months and a pond scum bloom is bound to happen. A common issue with declining natural ponds or farm ponds is pond scum because of the high nutrient levels these ponds tend to accumulate. In backyard constructed ponds and water gardens pond scum will occur for the same reasons (high nutrient, light exposure, high temperature) but the cause is usually due to poor pond management (over-feeding, over-stocking, dirty filters, excess debris in pond); or poor filtration, which is a rampant problem in backyard ponds with the majority of constructed backyard ponds being under filtered.
What can you do about pond scum? Depending on the type of pond you have and the particular circumstances around the pond scum problem, there are different approaches to control or eliminate a pond scum problem in your pond.
For the natural pond many choose to utilize chemicals to kill the pond scum. Chemical treatment is quick, easy, fairly effective, and not outrageously expensive. However, chemical treatment, in my opinion does not really address the issue; it just hides it until later when the same issue floats to the surface again. My preferred approach is to diagnose the reason, the source of why the pond scum is occurring and attack the source of the problem. This could be as simple as not putting grass clippings into the pond, or redirecting some of the groundwater run-off. Treatment could also mean a good cleanout of the pond via dredging or manual cleanout of debris and installing aeration, or some type of filtration for the pond. Sometimes even adding desirable nutrient loving aquatic plants to the pond will resolve the problem. Treatment approaches such as pond shading also help to reduce pond scum returning. The proactive of supplementing ponds with beneficial bacteria treatments, or barley straw (extract) treatments can help improve water quality tremendously. These types of approaches actually deal with the source of the problem and provide long term solutions to controlling pond scum.
For the constructed pond or water garden it is often as easy as a good cleanout of the pond. Some other ways to get rid of pond scum is upgrading filtration, adding aeration, increasing circulation, reducing stock, controlling your feedings, installing or adding aquatic plants to your pond. The backyard pond is certainly a much easier fix for the problem of pond scum.
The good news is that pond scum is easily treated and defeated with the help of a pond professional. Even ponds that seem “too far gone” can still be brought back and restored to the natural beauty they once held. Remember the basics: diagnose the source of the problem, then take the steps necessary to correct that issue, and make use of your local pond professional for advice and services.
The LOVE YOUR POND blog is written by Mike Gannon of Full Service Aquatics. Mike is a professional pond builder and expert in the broad topics of fishkeeping and water gardening. Mike also produces THE POND HUNTER video series which can be viewed on Youtube. “In The Pursuit Of All Things Aquatic” the Pond Hunter videos provide how-to pond construction videos, pondumentaries, and videos of related interest. Mike resides in Summit, New Jersey with his wife and 2 daughters. To visit his website go to and visit The Pond Hunter at

Written by admin


    Comments Feed
  1. Andrew Wilson Says:

    on June 22, 2011 at 2:15 am

    I’ve done all the things you suggested (no fertilizers, no soil, clippings get washed in, very few small fish, oxygenating plants, new pump, filter, UV) and the surface scum remains as bad as ever. I’ve also done barley straw extract and while it cut down the scum a little, the pond still looks awful. Only time of day that it looks fine is early i the morning. As soon as the sun hits, the ‘s ‘ rises!
    I need new ideas – desperately!

  2. Mgannon Says:

    on June 28, 2011 at 9:18 pm

    Hello Andrew, can you send me some information on your pond. Maybe I can make some more suggestions not covered in the blog post. Thanks for checking out the blog!

  3. Mark Pearl Says:

    on March 30, 2013 at 5:50 pm

    I have the same issues as Andrew Wilson describes above. It’s only 3/30 and the scum is already awful. It’s only in the 50s, can’t imagine what it will be like when the temps hit 90. any help would be greatly appreciated.

  4. Adam Says:

    on July 4, 2013 at 8:21 am

    Any answers to the above questions from Andrew and Mark????? I too have the same issue.

  5. Brent Says:

    on July 13, 2013 at 1:10 pm

    I have a green scum floating in my bass pond. My pond is about 1.5 years old. I have a pump that aerates my pond….should I leave the pump running or turn it off in order to get rid of scum? I need help

  6. Mgannon Says:

    on July 15, 2013 at 11:38 am

    Hi Brent, I’d recommend leaving the pump running to keep oxygen levels higher which will help to reduce algae growth. Thanks for checking out the blog!

  7. Mgannon Says:

    on July 15, 2013 at 11:52 am

    Most pond scum and algae formations will be due to excessive nutrient levels. Site conditions for each individual pond can have an impact on water quality so a site visit usually helps give much better suggestions, however; sight unseen I’d say that aeration and beneficial bacteria treatments can and will reduce and slow algae growth. Submersible aeration works best but a floating aerator helps too. Some other strategies will be more costly but creating a skimming zone in your pond will also do a great job of helping to clear the surface of the pond and increase oxygen levels. Other types of filtration could be employed such as wetland/bog filtration system. Adding plantings to the pond will also have an impact via of competing with algae for food sources. Often times a multilevel approach to reducing and controlling algae si necessary for natural ponds. If any of you would like to discuss in more detail feel free to give me a call (908) 277 6000, the more info I have on your particular pond will help me to tailor some suggestions for you. Thanks for checking out the blog!

  8. J. BARTON Says:

    on September 4, 2013 at 5:56 pm


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