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How Do I Get Rid of this Terrible Odor Around My Pond? – Pond & Lake Q & A


Picture of Gas Being Released from the Pond.

Pond & Lake Q & A

Q: I have an awful smell around my pond. What is causing it and is there anything I can do to get rid of it? – Hailey of Nebraska

A: I think we’ve all experienced this at one time or another. We’re outside, enjoying the spring breeze and decide to go wandering around the pond to maybe spot some frogs or to feed the fish. All of sudden you go to breathe in the fresh air and you quickly realize that it’s not so fresh after all. Your nostrils are engulfed with a distinct musky odor as you retreat away from the pond. Is it gas? Do you call the fire department? No. Call The Pond Guy. That sulfurous smell that finds its way around ponds is a common byproduct of a pond that is not aerated.

Non-aerated ponds stratify (layers in the pond have distinguished temperature differences) in the summer and winter, locking the bottom layer of water away for months. With no circulation, the oxygen is quickly used up down there, resulting in an anaerobic (functioning without oxygen) digestion process that is loosely equivalent to that of a cow’s stomach. Slow-moving anaerobic bacteria on the bottom use enzymes to ferment and digest the muck on the bottom. These bacteria produce waste products including carbon dioxide and hydrogen sulfide (rotten egg smell).

Most of the year, an un-aerated pond will smell fine because this buildup of nasty gasses stays locked away on the bottom. It is when the pond turns over (Spring/Fall temperature shift, strong weather event, etc.) that the foul-smelling gasses are released. Surprisingly, the foul smell is the least of the pond’s problems at this point. The release of this gas also signals that the inhospitable water that was stuck underneath has now mixed into the upper part where your fish are living. Wacky pH shifts, dissolved oxygen crashes, and algae blooms are a few of the byproducts of turnover, all of which have fish-kill potential.

The solution? Aerate like it’s your job! An Airmax Aeration System will keep the pond in a permanent state of motion, continuously venting gasses and providing oxygen to the bottom sediments. This allows the aerobic (good, oxygen loving) bacteria in the pond to inhabit the bottom sediments and work away at that ugly muck layer. Aerobic bacteria work similarly to plants in that that they use up the bad gasses and muck, and give off a little oxygen in return while working much more quickly than their anaerobic (cow’s stomach) counterparts. Supplement these bacteria with MuckAway or PondClear bacteria that will accelerate the decomposition process. Remember, keep that pond moving to keep that pond healthy and odor free.

POND TALK: Have you ever run into this odor problem? Tell us about it. What are you doing or have already done to get rid of it?

19 Responses

  1. We live a few feet away from a man made pond (formed by a dam on a river). This summer, the dam owner is emptying the pond to repair the dam. Process would take ~ 3 months. What impact should we expect? (smell, animals, etc.) Anything we can do to prevent / mitigate the impact? Thanks

    • You may notice that some of the wildlife moves to other locations temporarily and will mostly likely return once things are back to normal. If muck has been accumulation you will probably notice some odor from rotting material being broken down. Raking out any dead debris will help to reduce this when water returns to the pond but nothing else needs to be done without the pond being full of water.

  2. Hi,
    I just recently built a 6-7k gallon koi pond which currently has no fish in it as I figured I would wait until the spring before introducing fish to the pond. But there are two ducks that have access to the pond. I still have my pumps and two large aerators going even in these winter conditions (low around 25F today). The pond hasn’t frozen completely over since I have these aerators, pumps and a biofilter/waterfall that continues to oxygenate the water but today I noticed a strong sulfur smell emanating from my shed which is next to the pond edge which houses the Pondmaster aerator. Today, the pH is 7.6-7.7, Ammonia is 4ppm, nitrate and nitrite is both 0. I assume since the water is just above freezing, the bacteria in my biofilter hasn’t quite grown into the numbers that it needs to handle the waste from the ducks. Also, there are no plants in the pond. In this situation, what can I do to lower the ammonia level and rid of the sulfur smell? Also, I have added approx 200lbs of solar salt over the course of the past 4 months to the water to create a briny water so I havent needed to heat the pond all that much. Please advise me on how to proceed. Thanks.

    • In the cold winter months there is little you can do to establish much bacteria growth, keep the circulation going and rest assured that the bacteria will begin to increase as it gets warmer. Since this is a newer pond it looks as though your pond is just going through its natural establishment cycle. You may see the ammonia continue to increase and then it will decrease at which time you will begin to receive nitrites. Once nitrites have risen and fallen you will start to see nitrates. At this point the pond has cycled and will be ready for your fish!

  3. aeration is the best solution. Potassium permanganate may be one of methods to reduce odor.

  4. HAVE A ODOR PROBLEM WITH A LARGE POND AND WATERWAY.
    NEED HELP PLEASE, PLANTS IN POND IS CHARO

    • Hi Bill,
      Chara is not a pond weed but a form of algae. There are a few distinct qualities for Chara, which separates if from pondweeds. Chara has a “skunky” or musky smell, which you could smell if walking close by the pond and Chara is not rooted into the pond, like pondweeds and it is very easy to pull out of the water. It also has a very gritty feel when you rub it between your fingers.

      It would require an algaecide, such as Cutrine Plus Granular for treatment. If you are on a waterway that connects to public water, you would need to check with your Department of Environmental Quality or DNR for any permits that are required and what chemicals that you are allowed to use.

      I have also included a link to another Pond Blog question that discusses odors that are not related to Chara.

  5. I have a water fountain in my office at work; and I’ve been trying to find some kind of solution to help with the smell. When I leave for the day I turn the fountain off and back on the next morning, however on Fridays when I leave for the wkend and come back in on Monday’s the fountain smells like rotten eggs when I plug it back in. This is bad for our clientelle. Any suggestions? I called Lowes and have tried several things but I would really like someone who know what their talking about to help. THANKS

    • In regards to the rotten egg smell in your water feature, this is most likely caused by a build up of organic debris that is slowly decomposing. Has anyone done a clean out of the fountain? Products such as Barley Straw Extract and Liquid Clear will also help to remove the build up of organic material and reduce the rotten egg smell. If you like you can respond with more details about your fountain and we can provide further recommendations. Some helpful information would be the setting (indoors or outdoors), if there are any fish present in the feature and approximate length and width of the basin containing the water or approximately capacity of water. You can also click on the product names above for a link to the products on our website.

  6. i bought my house 2 years ago and the people before didnt take any care of the pond at all.at the worst spots there is about 2 ft of muck the pond is about 3/4 of acre i am trying to do what i can with a fountain and chemicals but its so mucky i cant tell the results should i keep in one area? we would like to use this pond to swim what are your sugestions? thanks

    • As for the muck, I would start by raking out as much as you can first using a Pond & Beach Rake. After that you can use MuckAway to continue to breakdown muck and other organics in the pond to help prevent future buildup.

      As for the fountain, they are usually best placed in the center most part of the pond if you are trying to use it to aerate, however, fountains are not the best aerators when the depths of your pond are deeper than 6′. If this is the case I would utilize the fountain for more of a decoration and use an Airmax Aeration System to aeration and circulate the pond.

      Hopefully this helps.

  7. Sure, aeration helps a lot; but unless you fix what’s causing the problem, you’re probably wasting your effort. Think about why there’s stink in the first place. Most probably your pond is overfed with N and P leaching from the fertilizers that makes your lawns green. I aerated, added beneficial bacteria, and stopped using fertilizers. Did this for 2 years. My pond has been stink free and the water clear for at least 3-4 years since. Now, I don’t even aerate. Just don’t feed the pond!

    • Tony,

      Great comment, my only thought is to keep aerating for the overall health of the pond and more importantly the fish. Other than that you are absolutely right, don’t feed the pond or keep it at least to a minimum.

      • What do you mean by “don’t feed the pond”?

      • Julie,

        What I mean by feeding a pond is simply limiting the amount of organics that go into the pond in the first place. For instance grass fertilizers for your lawn, grass clippings from cutting the grass, leaves & twigs that fall from the trees. These organics, once they get into the pond, begin to breakdown into “muck”, which is what we were referring to above.

        Hopefully that makes sense. Thanks for the comment!

  8. I have an odor around my pond sometime and my pond is aerated. What could my problem be?

    • Richard,

      Another possible reason for the odor smell with be from a form an algae called chara. Chara has a musky smell to it and at times can be pretty smelly. I would walk around the edges of your pond and look for something that looks like this: Chara

      Hope this helps!

  9. Do you know an good dock suppliers?

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