About 7 years ago I started developing various water features, both garden ponds and water falls. As part of my research I found consistent comments like the following: you can’t make a natural pond using a pond liner without pumps and filters. The use of the word ‘natural’ here refers to the pond filtration system, not the esthetic look of the pond. I’ll deal with esthetics in a future post on how to build ponds.
In a natural pond the water, soil, plants, and animals all live in harmony. No one comes along to clean the pond or to aerate it. There is no big man-made filtration system that keeps the water clean. The common advice is that a pond liner is artificial and a pond built with it will never reach a natural state where the water, plants, and animals live in harmony the way they do in a natural pond. If you don’t filter such an unnatural pond it will become full of algae and the water will be dirty and smelly. The only way to have a pond with a liner is to add aeration and filtration.
Is this really true? Do you need pumps and filters to provide artificial pond filtration?
Building Natural Ponds
This blog post is the second most popular post ever on this site. Lots of people comment and are interested in more information about building natural ponds, so I have started a public Facebook Group to make it easier for people to discuss this hot topic. Please join the group at https://www.facebook.com/groups/1760349757565562/
What Happens in a Natural Pond?
In a natural pond animals (insects, fish, etc) eat, poop, sleep and die. Both the poop and dead animals add nutrients to the water. Some is added immediately, and some is added over time as the material is degraded by various micro-organisms.
Plants also add nutrients when they die. In fall all kinds of leaves and other dead plant material is blown into the pond, and as this material is decomposed by micro-organisms it also increases the nutrient level.
Algae is a plant that grows best with high light and high nutrient levels. When the nutrients get high enough, the algae takes over the pond and chokes everything else out.
Why does the algae not take over natural ponds? The answer is higher order pond plants (not including algae). Plants also use nutrients and as long as the plants in the pond use up the nutrients as fast as they are produced, algae has trouble getting a foot hold.
The secret to an algae fee pond is to control nutrient levels!
The other important part of a natural pond is the presence of micro-organisms. They are everywhere; in the soil, on rocks, and attached to plants. Think of these micro-organisms as the ‘cleaning machine’ of the pond. They take rotting, smelly animal and plant material and turn it into nutrients that plants and algae can use. The micro-organisms keep the water clean, and keep it from smelling.
A man-made pond made with a pond liner has no soil – so one source of micro-organisms is missing, especially if you keep cleaning the pond liner. Most ponds have few stones and few plants reducing the number of micro-organisms even further. Without microbes or filtration, the dead animals and plants just sit in the bottom, making the water cloudy and smelly. But it does not have to be this way – read on.
Controlling Nutrient Levels
There are a number of ways to control nutrient levels:
1) Don’t add too many fish. Too many fish results in too much fish poop. Koi poop more than gold fish.
2) Don’t feed fish. There are lots of natural things for the fish to eat. Adding extra food just adds more nutrients to the pond.
3) Have lots of living plants in the pond. With enough pond plants growing, they will remove the nutrients before the algae can grow.
Most man-made ponds are not designed to hold a lot of pond plants. Without the plants you need to add some type of mechanical filtration system.
The picture shows a pond at Aspen Grove Gardens during installation. The black pond liner is in the deep part and the planting shelves are covered in carpet (white/gray areas). The liner will be pulled up to cover the carpet.
Note the extensive size of the planting shelves compared to the total size of the pond.
Why Aerate a Water Feature?
A natural pond has no obvious aeration. There is no hidden pump creating air bubbles. So why is it needed in a man-made pond?
A poorly designed man-made pond does not have enough plants, and it does not have enough places for micro-organisms to live. As a result, dead stuff accumulates on the bottom. As this dead stuff starts to rot it uses up oxygen, and the water at the bottom becomes depleted in oxygen, which in turn causes anaerobic bacterial to grow. This type of bacterial loves the smelly mess and they thrive with low levels of oxygen. This seems like a good thing, and environmentally it is a good thing. The problem for us is that as they digest the rotting stuff, they make the water smell. We don’t like smelly ponds even if they are natural.
How do you get rid of the anaerobic bacteria? Simple, increase the level of oxygen by pumping air into the water.
Aeration is recommended for ponds so that they don’t smell and that works quite well. The problem is that without anaerobic bacteria, the sludge on the bottom degrades very slowly and so you also need to clean the bottom of the pond on a regular basis.
Think about this. Because you bought a pump and you aerate the water, you now need to do more work and clean the bottom.
Do Natural Ponds have Smelly Sludge at the Bottom?
Sure they do. It is quite normal to find this in a pond where a lot of animal or plant material falls into the water. You don’t normally smell it because the water is not stirred up enough to move the smells to the surface. Dig around with a shovel or step into it from a canoe and you’ll find the smell. The smelly sludge on the bottom is natural.
My man-made water features have sludge and anaerobic bacteria in the bottom. If I don’t disturb them, they degrade dead plant material, and produce nutrients for growing plants. In my ponds I don’t stir up the water so I don’t smell them.
Pond Filters
Virtually every reference on building water features recommends some type of filtration system for a man-made pond. Why is this necessary?
As mentioned above, the lack of soil in the bottom of the pond and the lack of rocks and plants results in an environment that houses few micro-organisms when compared to a natural pond. The solution is to provide a man-made place for the microbes to live. Most filtration systems contain some type of surface for the micro-organisms to live on. This can be sand, wool, small pieces of plastic – it doesn’t really mater. What is important is that there is a lot of surface area. Microbes like to attach themselves to a surface and then ‘eat’ plant and animal bits as they float by in the water. So the filter replaces the natural places were microbes live–on soil, rocks and plants.
In nature the microbes live in the slime you find on rocks. It is healthy for a pond.
Water Feature Myth
The above information should give you some background to understand both natural and man-made ponds. If you think about it for a while you will realize that a properly designed pond, with enough pond plants and homes for microbes, should work just as well as a natural pond. When I was planning to build my ponds I spent a lot of time trying to find a reference for a man-made pond that worked without pumps and filters – I found none. Every reference I found said that such a pond will not work.
I set out to prove the experts wrong.
The following is not the result of good research or the opinions of experts. It is the result of my experience with two ponds over a 6 year period. In this blog I am not describing how to make a pond but I will do that in another blog entry–some day. I will provide the key points to consider.
Based on the information above, a pond design needs two things which are lacking in most designs. It needs lots of pond plants. Plants will use up the excess nutrients and keep the algae in control. It also needs lots of little homes for microorganism – they will help keep the water clean.
The following are some key design decisions:
1) Wide planting shelves. My pond is 20 x 30 feet and about half of that area is in the form of planting shelves that are about 8 inches deep.
2) Soil is not used for the plants. Pond plants don’t need a substrate, except to hold them down, and the pond certainly does not need more nutrients from soil. The plants should be using the nutrients produced by the micro-organisms and not the nutrients in soil . Instead of soil, I use small rocks – 1/2 inch or so. I just use all the small rocks I collect as I make new flower beds. Don’t fertilize your plants.
3) Pond plants are not in pots. I just place them on the small rocks in the planting shelf. A larger rock on top holds them in place until they root.
4) The sides of the pond are lined with rocks adding more surface area for microbes.
5) A deep planting shelf (about 2 ft deep) is also present for waterlilies. It is important to cover 2/3 of the surface water to reduce light getting to algae.
6) Goldfish were added to feed the plants, and eat mosquito larvae . They are never fed. They grow quickly and breed regularly.
The garden pond in the pictures was built 5 years ago and it is only now that the planting shelves are starting to be full of plants. Wild bull rushes seeded themselves the second year. Irises have been added and are spreading. The pond has never been drained, and the bottom is never cleaned. It has no pump and no filter. Wind is the only thing that might provide some aeration as it ripples across the surface of the water. There are several large trees around the pond that add fall leaf drop – which is left to settle in the pond.
For the first 4 years the pond plants increased in number each year. During this time, I did have string algae, but it mostly had a spring bloom and by mid summer it was under control. The water was very green showing the presence of lots of one celled algae, but the water was clean, and it did not smell. The fish that were added the first year did not over winter but since year two they have overwintered and keep breeding. Herons and racoons help to keep numbers in check.
From a naturists point of view the pond is very healthy with lots of frogs and dragon flies breeding each year. Larger mammals, including deer use it as a water source.
It is now nearing the end of summer 2013 and the pond has been extremely clean–much clearer than the picture below from 2012. In fact it is too clean. You can now see the pond liner in the deeper sections of the pond. There was no string algae this year and almost no one celled algae. It has been a strange year weather wise which may account for some of this, but I think it is mostly due to the fact that the planting shelves are now very full of hungry plants which are out-competing the algae.
After 5 years I conclude that aeration and filtration are ‘probably’ not required. I’ll need to wait another 5 years or so to be absolutely certain of this. It is possible that in a few more years the stuff at the bottom will overwhelm the pond and may need to be removed. I doubt it!
String algae is gone, but one celled algae is still making the water green in late summer. Note the number of plants in the water.
As plants grow and get larger, algae is almost non-existant.
Is Green Water Bad?
From an environmental point of view there is nothing wrong with water that contains algae. In a natural pond it might indicate that too much fertilizer has leached into the pond which is not good. But this is not usually a problem in a man-made garden pond. If your pond water is green with algae it is probably healthy.
You might not like the look – that is a different matter.
In Japan, garden ponds are treasured and it is common to buy a dye to color the pond water. Why do they do that? When the water is colored it reflects light much better. The shadows and reflections are considered to be very desirable. So next time someone comments about your green water, just tell them that you do it on purpose to better enjoy the reflections.
If You Have Questions
If you have further questions about building natural ponds or about your existing pond please post them in our new face book group called Building Natural Ponds.
Beneficial Pond Bacteria
natural ponds do not need to have bacteria added. For more on this topic have a look at Beneficial Pond Bacteria – A Waste of Money.
Related Posts
Winterizing Ponds and Water Features
This post is so helpful! My family just purchased some land in central Florida that contains a small man-made pond (maybe 12 feet by 6-7 ft, about 2 ft deep). The pond has never been filtered before, but through our hot, muggy summer it has become very green and opaque. Everyone that I have spoken to says it needs a pump and filter. I have no idea how the previous owner cared for the pond, but I know he did not have any filters or pumps. I want to return the pond to its former beauty, but would like to do it as naturally as possible. Is this possible in steamy Florida? Where do you start if the pond is already slimy green? Thanks in advance!
Add lots of plants.
Robert you rock! I’ve been holding down my own self-made small pond this spring/summer with no filters or pumps. Your blog has inspired me for new work to begin next spring ie the planting shelves/carpets.
I love the quiet and stillness of the pond and sit by it regularly for meditation. Are your gardens open for visiting? I am also in SW Ontario 😊
My garden is private and not usually open for visitors. I do host gardening groups.
Robert, perfect article.. I am in suburban Melbourne Australia.. we have a basic pond with goldfish, they get so big…. (even too big for the ducks as they do visit) and they breed away..therefore all must be happy.. maybe too happily breeding as our pond is now a light green and I cant see through it.. will plants be enough to clear it a bit.. we have pot plants on the bottom with plants.. just not sure we have the right ones?
appreciate any suggestions.. Denise.
If the algae grows there is either not enough plants or too much organic matter like fish poop. The type of plant is less important than the quantity.
I want to start small with a middle sized fish pond. This was a super good read because I was just about to make a bunch of mistakes haha. Thanks for the super good comments too. I was wanting to keep tropical fish in the pond but heating it in the winter would be nearly impossible to do I guess.. sort of makes me sad but maybe I can find some cool cold water fish.
You can heat the pond – but it would cost an arm and a leg in cold climates.
Complete novice here, now feel like I know a little something – which is a new concept. Many thanks for posting your (sorry, some of your) experience on here, it helps us a lot. Looking at creating a fish pond on a sloping garden with zero artificial involvement (electricity, fish food etc) and a glass viewing window. Why start easy?
Thanks from Yorkshire, England.
This was an awesome article – very helpful as we have just bought a house in the country with a naturalized, man made pond. Q: Will a dog swimming/going in and out of a man made pond create problems for the pond?
I doubt it. In the country all kinds of animals will use a natural pond and cause no problems.
You do want to make sure you have a beach area where the dog can easily get out.
Great Post. Thanks. Do you know how much water you lose from evaporation? In the summer, how much refilling do you need to do?
Lots of variables affect this. In my large pond, with normal rain fall, I only top it up once a season. This year has been a drought and I topped it up twice.
Hi everyone. I read comments and it looks like a lot of people have gold fish. We have a broken swimming pool here and one of my flatmates put two gold fish there. Water levels are low. I saw one after 6 months his size doubled! Not sure what happened with the other one. Maybe died, maybe some of the birds cauth him (there are plenty of them here). The hole looks horrible and full of algea but fish can leave there and grow. Gold fish look like a really tough ones. But what about trout? I’m living in Australia atm and going back to Russia in Novemer. I want to find a land and build a pond and grow trouts there. I’ve read many resources and all of them say that you need running water, trouts don’t reproduce in ponds (only if you make it work like a hatchery but not a natural pond). Is that true? Does anyone have experience growing trout in a “natural man-made pond” ?
Trout need cold water. They do not breed in ponds. Most people who have trout buy baby trout and add them to the pond.
My new book “Building Natural Ponds” includes a chapter on larger natural ponds suitable for trout and other game fish. Expected release in spring of 2017.
I did some reaserch and some people say that it is possible for trout to spawn in a pond if there is is shallow beds of gravel . And I’m really confused now. Maybe I should try to make a small experimental pond and put a few trouts and see how it goes? I know I can’t trsut anything I find in internet.
Depends on species. Some species of trout absolutely do breed successfully in stillwater with the right conditions.
I had a hole dug..about 75′ x 23′ x 4-7′ deep and put in a liner two months ago. Because the hole diggers didn’t get it level the shelves are uneven with some deep and some shallow to totally exposed. I’ve started planting out the shelves with the only plant that can handle this heat, loose strife. It’s a beginning thing. A crazy storm added clay off of the hill which I am grateful for. I’ve added water lilies and, on impulse, 100 baby blue gill. Recently I added my two pet koi and a few of their babies. The heat out here is causing massive fish kills and I am fortunate to have lost only the catfish fingerlings and rosy minnows I bought from the fish truck. I’ve since added water fountains to mix things up and aerate. The water temperatures in the shallows are daily close to 90. My plan is to continue to add plants. I’ve got lots of frogs now and dragonflies too. It’s actually getting kind of loud out there now! It’s not safe to be in the sun too long at this time so it’s going slowly. My concern is that I may have inadvertently overstocked in regards to the bluegill. The fish truck lady told us a horrifying story about how they will get very big very quick and reproduce like rabbits!
Here are my questions:
1. Is the fish truck lady right and if so how do I reduce my bluegill population?
2. After reading your article I am aware that I need more plants asap. This takes time. The one plant that I can get which I know will grow fast is anachris. My friend has it in her pond. It is invasive there. I clean out bushels of the stuff yearly from that pond. I dread adding the plant to my pond but if you think maybe I need to get a quick plant boost, I will do it.
3. Thanks!
When conditions are right fish will breed. When they breed you may have the problem of too many fish which cause too much waste which results in algae growth. The only way to manually remove fish is to catch them.
Anacharis is a floating plant. It will remove nutrients and help keep the pond clean. I prefer using rooted plants on the planting shelves.
Karen, i just saw this post, but if you still have the bluegill, let me tell you that they are some of the best eating fish you can have! a nice palm size fish will fillet nicely and make a wonderful meal. where we live, i find they seldom reproduce in water that doesn’t have an area that is shallow, say 6 to 8 inches deep. hope everything turns out well for you.
I live in zone 4B in southern Ontario. Thank you for this article. Have you written a winterize your pond article. I would like to read how you do this. V
I have not – but will be writing several additional articles on ponds this fall.
Winterizing is easy. On my large pond I add an aquarium air pump to keep the ice open so that the frogs have a better chance of surviving. On my waterfall I take the pump in the house. That is it.
Great article, real glad we came across this. I have a pile of questions, hope you don’t mind. We are also in a zone 5 to 6 but not a lot of rain, 10 to 15 inches a year however the farmers are growing wheat, barley, canola, and such without irrigating. One of the goals for our pond is water storage to use for irrigating the gardens, so that I can manage the use of our well better, so in the 90 to 100 or so days of the growing season we will be pumping water out daily and topping off the pond strategically a few times a week with fresh well water. Do you foresee a problem with this?
What do we need to help get the plants started? Would it help to bring home a couple buckets of creek or river water?
Is there a proportion you would suggest for the area of shallow plant shelf vs. the deeper fish water?
Thanks for sharing, I wish I could wait for your book, but I’m all fired up now to make this happen yet this summer.
Using the water for irrigation will be no problem.
You don’t need anything to get the plants started. Bringing in water from a river might introduce diseases.
I recommend 1/3 to 1/2 of the surface area be dedicated to plant shelves.