Rotting plant matter and no filtration is the cause of the stink. As you say it smells like a swamp.
The smell comes from Hydrogen Sulfide being produced by the rotting plant material and soil. It is a natural condition in a swamp but should not be allowed to happen in a garden pond.
It will be a breeding paradise for mosquitoes.
"Horton"

Thanks. How do I deal with this problem (if you are correct)? Empty out the pond and clean everything? Or, is there some other solution?

Thanks again.

dln949

Yup, gotta clean it out and refresh the water, it's a yukky job but you will be happy in the end as it will seem like a new pond again!!! You will want to sit by it and enjoy it after all that hard work!!!

Cleaning it out is only a part of the solution. The smell and other rotten water problems will continue to occur unless you have some way to introduce oxygen to the water. Whether you intended to or not, you have made a home for microbes. Microbes in a plentiful oxygen environment consume nutrients in the water and keep it clear and fresh smelling. Microbes in an oxygen depleted environment produce unhealthy water, noxious gases and can eventually kill your plants. Plants that do thrive in such conditions are similar to algae but are slimy, stinky and not very attractive.
If a pump and filter are not possible, can you put in a bubbler? If there is no electric available there are solar devices although they are not very efficient. The only other solution I can think of is, in addition to persistent removal of debris, there should be a constant influx of fresh water as oxygen depleted water is removed. This can be very wasteful and expensive unless you have a rain water collection system such as rain barrels.
An important point that needs to be discussed here much more often is that a man made pond or water garden is a contained system that is not found in nature. A natural system survives only when it has a constant or persistent exchange of water from streams, artesian upwelling, rain or drainage.
One resource you should check is the Bog Forum here on Gardenweb. They might give you some additional ideas. Sandy

Thanks to all for the information. A few more questions:

In our pond I deliberately put in a lot of anacharis, hornwort, and parrot feather. I was told that they add a lot of oxygen. Is that not true? Or, are they just not able to produce enough?

We have a small pond, about 300 gallons.

dln949

like most plants the anacharis, hornwort, and parrot feather, use up carbon dioxide during the day and expel oxygen at night.
However the production of oxygen, from the so called "oxygenators" is greatly exaggerated.
They produce some oxygen certainly [and do help in shading and condition the water], but not as much as they are touted to do, by pond plant sales people.
It is another pond keeping myth.

In your situation, because there is no filtration/circulation in your pond, the anacharis, hornwort, and parrot feather, are actually helping to trap the noxious gasses in the pond.
"Horton"

Do you have plants in the pond that are potted? If so, what are they potted in?
Years back when I first started ponding I tried using the plain kitty litter to pot plants in. I know many people use it and use it successfully. It was a huge mistake for me. Within a couple of weeks I noticed this horrible smell when I would go outside. I finally realized it was coming from the pond. Since the pond was basically pretty clean I couldn't imagine why it smelled. I pulled up several of the plants I had potted in the kitty litter and the smell just about knocked me over. It was HORRIBLE!! So, I had to pull all the potted plants out, dump them out, hose them off and repot in top soil and pea gravel. That worked fine and I've been doing it this way ever since.:)
I'm not really sure why the kitty litter smelled so bad in my pond but it was really nasty. So, check your plants.:)

Horton, I fell for that! I put hundreds of those "oxygenators" at the bottom of our pond! Wonder if I should leave them down there or take them all back out? We are about to be filtering so maybe I should give them a chance??

If you have an abundance of them you could cull them a bit,
They do grow fast as the summer progresses.
You could also wash them with the garden hose, when you pull them out of the pond. That will wash some of the smelly bacteria off the plants.
Good to read that you are going to have some filtration it should make a big difference to the situation.
"Horton"

A pond without fish does not really need any filtration. You don't need to change out your water. Just provide the pond with some type of water movement such as a pump with a bubbler or fountain and net out the decaying debris that has settled on the bottom (doing so periodically over time).

Nance

I have six small ponds plus about that many small container water gardens with no filtration and no water movement that are full of plants and wildlife, had them for years with no stink, no stagnant water and no mosquito problems either. I use Mosquito Dunks. I don't clean them out all the time either.

I credit the anacharis and hornwort in my 900 gallon fish pond for keeping it clear for twelve years. The only time I had a green algae bloom was when I pulled up almost all of the anacharis one fall in a cleaning frenzy. That spring I had pea soup. I planted more anacharis and let it alone in fall and have never had pea soup again. Never had it before that either. I have a simple DIY filter in there, nothing more than some lava rock and mesh material in a mesh basket as a prefilter on the pump.

That's true enough, if you have enough wind movement you don't really even need a pump. A pump does however provide some beautiful sound effects!

And you know...some little varmint could have fallen into your pond and died. During periodic cleanings I've scooped out some very dead moles that found their way into the pond. Very gaggy indeed!

Nance

Dead earthworms and slugs reek too even though they are small.

All ponds will smell if you are messing around in the muck or dirt in pots but they should not smell while you are just looking at them. I had my bunco group over a couple weeks ago and we ate dinner by the ponds and no one noticed any swamp odor. I asked them after reading this thread.

"I have a simple DIY filter in there, nothing more than some lava rock and mesh material in a mesh basket as a prefilter on the pump" I think that is a contradiction to your original blanket claim of no water movement. Perhaps you might want to make what you mean to say a little more clear. You don't mention water changes either. Sandy

The bottom line dln949, is that you can do any of the suggestions given on this thread and your pond will soon be smelling like a rose. Our opinions may differ but all the advice given is correct. And it is correct because you have a watergarden, not a koi or goldfish pond. Add fish to your pond and it becomes a whole new ballgame and you would most assuredly be getting a lot more advice here.

Plants are nature's filters. Given that, I think filtering the filters is superfluous. But that doesn't mean you can't or shouldn't do it. Having extra filtration would give your pond a pristine look and there is nothing wrong with that. My pond at the moment is empty of fish. I pulled out the pump and have only my plants left to enjoy. I do have plenty of wind movement in the pond, lots of dragonflies and frogs etc. and so do not have a mosquito problem. I am not too fussy about cleaning but I do keep the pond bottom relatively clean and prune the dying foliage. I do not change the water but it's clear and natural looking. My plants are all green, blooming and growing. Personally, I like having a pump in the pond, not only because it adds oxygen but the magnetic sound it provides makes it so worth having, be it a bubbler, fountain or waterfall.

You could also change your plants. Try one of the many different varieties of lillies. Use some floating plants to help cover the surface area of your pond. If your floating plants get to be too many you can just pull some out and compost them.

Nance

Sandy, I have more than one pond. Way more than one pond.

My fish pond has the DIY filter and a pump and waterfall.
My greenhouse pond has a spitting cat statue and a tiny pump but it runs less than an hour a week. I only plug it in when I'm in the greenhouse looking at it.

My center pond in the front yard has three bubbling rock columns and a pump.

My other ponds, 14 of them if you count the whiskey barrels and other "pots" including three liner ponds do not have any filtration of any kind nor water movement. More than I thought I had but I just went out and counted...

I do not do water changes on any of my ponds unless I am using a shop vac which is rare.

All of my ponds are heavily planted except the bubble column pond and the greenhouse pond.

I am delighted your water gardens are successful. From your description they must be well thought out. I saw the photos of the amazing job your husband did on the columns. I think I commented on them at the time they were posted. I don't have a problem with any of your water gardens but you seem to have told us that we don't need pumps and filters if we have enough plants. Maybe that is true for water gardens in the Marine West Coast Climate but most of us don't live there. For us it takes real effort to overcome some of the problems that cause green water and other assorted problems. Just the rainfall alone in your area combined with low evaporation rates could make water changes less necessary especially if all but one of your water gardens has no fish. All I am saying is you should make it clear that you just might have some factors that make it possible for you to do without some of the things that many of us must have. If I tried to do my ponds and water gardens the way you do yours they would be stinking swamps when they were not bone dry from evaporation. With as many trees and debris from them as this yard has, I would be running full tilt from container to container just to try to clean it all out.
Sorry if you are offended but I have to stand by what I said. You should make what you say a little more clear or you will be misleading someone. Sandy

I'm not offended. You seemed to think I was talking about one pond in my post not different ponds.

I don't think my location has everything to do with successful ponding with no chemicals, UV lights or pumps/filters. I have plenty of online pond friends that also have similar success.

I had a water garden with no pump/filter in Phoenix Arizona too. It didn't stink.

My yard is surrounded by trees too, there are 60' tall conifers along the fence line that are the neighbor's and there is debris in all of my ponds. I find it sometimes causes string algae but not pea soup. I don't stress over the leaves and needles. I simply could not keep them all out nor clean them all out.

I do have to add water to my ponds.

Some people like to throw as much money/time at a pond as possible. Some people don't.

One of the good things about online forums is that people can read experiences from people around the world and adapt them to their own situation.

I think it is wrong to tell someone that they MUST go buy a UV or MUST remove the rocks in their pond or MUST go buy a pump etc. People have a pond built and they logon here and are told they just paid for a POS and they have to start over and it is really discouraging. I find it upsetting to read. It is one of the reasons I've spent much more time on other pond forums than this one but for some unknown reason, perhaps masochism, I have spent more time here lately...

I am surprised you feel that way about this forum. One of the things I have always liked about it is the fact that except where electric hook ups are concerned, none of the regular posters insists there is only one way to do something and that every pond is the same as all the others. The electric thing is a matter of safety and local code and is beyond our power to change.
Frequently you will find a number of posters here that agree on a particular subject and that isn't surprising. For many of us it is a matter of been there, done that. It worked or it didn't and this is the reason why. On the other hand while there are disagreements about the relative value of certain methods, I rarely see the absolutist statements you say you have found. Of course people like that do show up from time to time but they rarely stick around very long. It is too hard to acquire a following.
To go back a bit, that statement "this is the reason why" is important here. There is no autocrat here who claims to be the only valid source of information but there are lot of people who have extensive experience, often under many different conditions. They can truly claim to be experts who are more than willing to explain an answer. Often you will see them direct someone to different resources or to links that can help with a particular problem if they do not have an adequate answer.
I have been to several other ponding forums, too. Some are dismissive of anyone who might have an experience differing from what is acceptable to that forums "experts". Some are flooded with neophytes who pass on incorrect information. Others are just plain ditsy with methods that have no reason to succeed. Then there are the ones who drown you in technical or "scientific" jargon which gives them an ego boost while smashing yours. Take your choice. I like it here. Sandy

I happen to love all the variety of suggestions I've gotten here.

all i want to know is the person who live next door to has 6wks ago put a hole in the ground, and put water into it, no plants, nothing, just a hole with a plastic sheeting in and added water, and put a stupid sprinkler in,today we asked her if she would turn off the sprinkler as it sound like a bust water main and at nite because it right near my window is annoying,she said she carnt as the water will smell,but its only from 10 pm to 9am,surley the water wont smell if the sprinkler has being turned off please help as im sure its an excuss not to turn the darn sprinkler off,

lol. Ear plugs might be an effective option

I have a pond that is completely choked with plants so am cleaning it out ad installing a pump and probably a filter too. I want to know if all the yucky plant life and dirt etc would end up being good compost if dried and mulched?