By: Mike Gannon | Posted On: October 18th, 2010 | 28 Comments on HOW TO GET RID OF POND SCUM | 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.

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Written by Mike Gannon

Mike Gannon

The LOVEYOURPOND Blog is written by Mike Gannon of Full Service Aquatics located in Summit, NJ. Mike is an award winning pond, water garden, and water feature builder. Always “In The Pursuit Of All Things Aquatic” Mike has been a lifelong hobbyist and providing professional services since 1995. Mike is the creator of The Pond Hunter video series seen on Youtube and has made several television appearances on Networks such as HGTV and the DIY Network. He also hosts the Pond Hunter Radio Broadcast, a show on everything aquatic, every other Wednesday at 8pm EST. You can see what else Mike is up to at the following sites:

    28 Comments on HOW TO GET RID OF POND SCUM

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  1. Mike Gannon Says:

    on March 1, 2019 at 8:47 pm

    Hello Rosina. I want to suggest you check out this blog I wrote on fish spawning. It sounds like you may possibly be dealing with a spawning situation!!

  2. Rosina Says:

    on February 24, 2019 at 1:20 pm

    Hi I have a 6′ or so deep brick butyl lined pond. Some of it it above ground and October last year after years of nothing in it as the Koi had been killed by severe Winter weather after 2/3 years, we decided we’d introduce Goldfish. So we bought 8 tiny ones from our local Garden/Pond Centre, floated the bags and then released them with this bag water into the pond. We had hoovered the pond out a month beforehand and for 10 years the water has been clear. We have a submerged Oase Pump, a UV filter and also a Pond Skimmer going 24 hours a day. Suddenly the pond is covered with green, foamy,scum which I tried to remove by hand without success. To stop the Heron we also have the Pond area mostly covered by ring/oblong shapes sold for that purpose. Have the fish or fish water brought this with them? No food given as yet and not seen the fish since last Autumn when we put them in except one one day for a minute or so about a month ago. Many thanks Mike – very frustrating as skimmed by hand and still mostly there.

  3. Mike Gannon Says:

    on August 1, 2018 at 11:50 pm

    Hello Bob. Yes, I’d run the fountain full-time until you start seeing some real results and then you can adjust the hours as you see fit. -Mike

  4. Bob Says:

    on July 31, 2018 at 2:58 pm

    I have a fountain running 12 hours a day, and i am having some periodic algae blooms. Should i leave the fountain on 24 hours a day? My lake is 10 acres. Thanks

  5. Mike Gannon Says:

    on July 12, 2018 at 8:43 pm

    Hello Steve. I’m glad to hear the grass carp worked out well. The algal film is probably from the fountain starting to stir up the pond a bit and getting nutrients stirred up causing a bloom. I would say it should be a temporary condition, however; if you’d like to send me some photos or video that would help me give some better feedback. Thanks for reaching out. -Mike

  6. Steve Burge Says:

    on July 11, 2018 at 10:30 pm

    Hey Mike, I bought a home approx. 4 years ago with a small 1 acre pond in the back yard – full of largemouth bass, Channel & Speckled catfish, 3 types of bream, and white crappie. Last fall I added 10 grass carp approx. 8-10 inches in size based on what the local feed and seed retailer/fish supplier advised to assist in algae control – this worked beautifully – approx. 2 weeks ago I added a small 1/2 hp pump to add much needed aerating to the pond – since adding the fountian, (another question I have is should I be running the fountian 24-7?getting mixed answers on this) I have a green film over approx. 1/2 – 3/4 of the surface of the pond that showed up almost overnight – the reason I added the fountian was because the water turned dark this year (really dark tea color) and I was afraid the pond would flip and kill all the fish – I treated the pond last fall for algae/weed control and the water was clear – not so much this year – any ideas? I have pics and a video of the fountian I could send you to see more of what’s going on – Thank you in advance

  7. Mike Gannon Says:

    on May 21, 2018 at 11:32 am

    Hello Denis. Getting as much aeration in there as you can is desirable. I’d suggest using some beneficial bacteria treatments on your pond, and yes, perhaps some barley extract. Both of these items are easily found on internet through pond retailers, a Google search will offer up some sellers of these products. Thanks for reaching out! -Mike

  8. Denis Says:

    on May 16, 2018 at 4:20 pm

    I like your suggestion of a multi-pronged approach. I drained our ground-water fed pond and removed most of the sediment along the bottom last fall but that doesn’t seem to have helped. I leave the waterfall running hoping it will aerate. We’re hoping at the water lilies mature they will suck up excess nutrients. You mention some chemical treatments and barley extract. Where can these be obtained?

  9. Mike Gannon Says:

    on April 3, 2018 at 12:39 am

    Hi Carter! I’d like to help but would need much more info to really give any sort of feedback. Tell me more about your pond. -Mike

  10. Carter Says:

    on March 7, 2018 at 4:14 pm

    Our old pond has been clear and perfect for many years. Last Fall, a neighbor shared some of his bass from his pond with us. About 10 fish and water from buckets from his pond. This spring, algae everywhere. Coincidence? I will remedy the situation, but want to understand why the change thus year.

  11. Mike Gannon Says:

    on September 20, 2017 at 6:27 pm

    Floating surface algae is indeed very difficult to remove!

  12. Gordon Drake Says:

    on September 18, 2017 at 11:56 pm

    I was told to drag a plastic snow fence across the pond up onto the shore and the scrum will stick to it.Nothing else works.

  13. Mike Gannon Says:

    on September 20, 2017 at 6:34 pm

    Hello Rose. How can I help? Thanks, Mike

  14. Rose Maier Says:

    on September 15, 2017 at 4:53 pm

    We just acquired a property with an old strip pit. It’s a very large pond, approximately 2 acre in a z shape, tall trees surround it and it has blue gill, bass, carp and not sure what else. Oily scum is covering it most days. Lots of trees have fallen over into the pond and you can only get close to the water on one side. Help

  15. Mike Gannon Says:

    on June 29, 2017 at 11:00 am

    Hi Sarah, thanks for reaching out. I’m sorry but I’m not too sure about what you are experiencing. Feel free to email me directly and maybe send some photos and I may have some better feedback! Thanks. Mike

  16. Sarah DICKERSON Says:

    on June 26, 2017 at 11:30 am

    My father built this Pond 40 years ago we have large grass carp koi fish that are 25 years old in it along with regular fish all of a sudden new black fungi silty things floating on top any idea

  17. Mike Gannon Says:

    on September 25, 2016 at 8:29 pm

    Hey Gard, thanks for the feedback! -Mike

  18. L Gard Says:

    on September 25, 2016 at 3:11 pm

    I have had a pond for 5 years, I use Blue Bayou color it keeps the sunlight out, (previous owner said to use) I had a problem with cat tails. till I cut them below the water line and added Blue to water. 2016 I slacked off using it and now I have scum. I started using it once again and it is slowly clearing up. I hope this helps.

  19. Mike Gannon Says:

    on August 11, 2015 at 12:33 pm

    Thank you for checking out the blog! I too am unaware of tilapia helping rid ponds of algae! You should be able to find tilipia dealers online. Good luck and let me know if using tilapia works! -Mike

  20. Robert Holmes Says:

    on August 6, 2015 at 9:43 pm

    We have the same scum problem. We have put in several grass carps and still the algae is growing at a great speed. I was unaware tilapia would help in ridding the pond of algae. Where can they be purchased? I am very interested in purchasing and raising tilapia.

  21. J. BARTON Says:

    on September 4, 2013 at 5:56 pm


  22. 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!

  23. 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

  24. 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!

  25. 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.

  26. 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.

  27. 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!

  28. 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!

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