AquacultureBiological CleaningDamsFishLandNatural SwimmingPlant SystemsWater Harvesting

Constructing a Fishpond Dam


The spillway that sets the height of the water and allows for passive
discharge of surplus water during large rainfall events

We can build a dam to serve specifically as a fish pond and which can be designed to be more productive for aquaculture systems generally, compared with stocking an existing farm dam with fish. As most of the production occurs in the upper levels of water, a depth of under 2 metres allows you to feed and harvest the fish easily and bring them to a desirable size as quickly as possible. Using an example of the chicken tractor, infrastructure design can also be applied to fish to create a more intensive system where resources such as the animals’ manure are cycled and productivity is increased whilst benefiting the surrounding systems. The ideal style of dam for the purpose of fish production is the contour dam, which is dug into the side of a shallow sloping hill (on a reasonable flat landscape) with a dam wall of a semi-circular curve or a semi-square shape. The profile of the dam floor can be easily constructed so that it is flat, and the inner walls and back-cut of the dam can be reasonably steep, maximising the volume and minimising the challenges of harvest, whilst maintaining a consistent temperature.


Large rocks positioned at waterline in the corners for
rod and line fishing for meal size harvests

Water quality: Water quality is an important factor in aquaculture, therefore it is not ideal to have the dam positioned on the water catchment itself (due to sediment runoff), but rather to gravity syphon or pump (if you have to) the water from another catchment. One of the inputs that raises the production is increasing the oxygen content in the water and one of the most passive ways to do this is to drop falling water from a height from one of the syphons from an overcharged uphill dam and/or swale system, which are often overcharged, so you can allow the surplus water to splash into the fishpond, oxygenating it in the process. An additional benefit is that as the water passes through the fishpond dam it collects additional nutrient from the fish and carries it further down the landscape. As the fish mature there is an increased amount of nitrite in the water from their droppings, which is converted into nitrate via the beneficial soil organisms.

Fish food: Another system input is food for the fish. Trees such as mulberries can be established around the pond to attract insects which fall into the pond, an ancient Chinese method. The mulberry leaves can also be inoculated with silk worm eggs which, once hatched, can be knocked into the pond. Crotileria grahamiana, a legume bush that grows well by the water’s edge where the soil is slightly anaerobic, attract the Monarch butterfly which lays its eggs on them and the caterpillars that cover these bushes can be flicked into the pond as fish food and the pruning used as mulch. There are many other types of tree that are suited to growing by the water’s edge that are also susceptible to becoming inundated by caterpillars, and they can be an asset in these systems. Solar lights can be used to attract moths and if the lights are low to the water the moths get trapped underneath and stuck in the water and it becomes a night time fish feeding system. Compost worm farm and vegetable waste systems can be set up to float on the pond to trap black soldier fly larvae as a direct harvest for the fish. Meat maggots can also be produced easily from dead animals, road kills, or meat wastes but the this can be quite odorous.

Water plants: Water plants are beneficial to have around a fishpond, as it improves water quality and gives additional habitat for fish. Water lilies, emergent plants and edge-side plants all have a an advantage in keeping the water clean and adding to the aquaculture ecology. Beneficial algae will naturally occur with sunlight and organic matter. The dam can be seeded with zooplankton by adding a bucket of mud from below the waterline of a good healthy dam, which only needs to be done once, and crustacea such as crayfish and particularly freshwater shrimp can be added which will feed on the zooplankton before being eaten by the fish. A way to tell if the pond is oversupplied with fish is if the shrimp population is greatly diminished.

Attachments and accessories: If you intend to keep fish that potentially run down stream in breeding times (like Australian Bass for example), you need to put a fence across the spill-way that is rounded out into the dam so that it doesn’t get clogged with vegetation etc during rain events. If you intend to stock eels (which would have to be trapped live as baby eels, or "elvers"), or to keep eels out, you need an eel fence (one that they can’t get through or over by propping themselves up). A platform or jetty where you can feed and/or catch fish from is a very handy attachment to a fish pond dam.


Stripping off the top soil from the site to be saved
and used to dress the site at the end

Construction: The construction process is much the same as any other dam, the first thing you need to do is strip the top soil off the area where the dam will be, including the dam wall, and put that to one side while you begin the construction process, this is used later to top dress the dam wall (and the back of the dam if there is a cut above the water line) so that it can be easily revegetated and thus restabilised afterwards. You then create the keyway trench by digging down in a slot shape below and along where the dam wall will stand until you get down to good solid clay (100% if possible).


Digging the hole and building the wall


Cutting the keyway below where the dam wall will stand,
to lock the dam water tight


Compacting the keyway trench by track rolling

As you start to dig into the dam, the clay from the main hole is packed into the keyway and rammed down very hard with track roll compaction or vibrating sheep’s-foot roller compaction (if you have marginal material that is a good process to use).


Track rolling the dam wall, to compact it until water tight

Dry material needs to be wet down. Once the keyway is dug and well compacted you have cut off any potential water flow going under the dam wall. The next process then is to dig out the dam main hole, using the material to build and compact the wall, making sure the inside and outside walls are not too steep (a 3-1 or 2-1 slope maximum) and are nicely compacted.


Flat bottom with a depth of 2.2 meters, ideal for a productive fishpond


Interns learn to survey the future water line accurately

The bottom of the dam needs to remain flat and perfectly level with a little over 2 metres as an ideal depth, allowing for a little bit of anaerobic soil creation on the bottom of the dam and an average of 1.5-2 metres of water depth for your fish.

Stocking the dam: Once the dam is built and filled with water from an uphill syphon, the next thing is to stabilise the dam and ensure a healthy dam ecology with algae (which will happen naturally from sunlight & organic matter), zooplankton (from a bucket of mud from a healthy dam), some crustaceans and water plants. You know when your aquaculture ecology is working well when the water becomes clear with 1-1.5 metres of visibility. It will always have a bit of a tannin look at first, but the clarity will increase. When this takes place you are now ready to stock your fishpond dam with fish. Your choice of fish depends a lot on where you are and what requirements you have. Here at the PRI on Zaytuna Farm we use Australian Bass, some eels, and local catfish, and they work pretty well all together.

Harvest: We often obtain a meal sized harvest simply using a rod and line and general fishing techniques as the fish are very easy to catch. We can also use a net, or lower the level of the water to harvest all the fish at once.


Fishpond dam wall with cover crop emerging


The back of the dam wall, with cover crop seed sprouting as the first
vegetative cover for stability and erosion control

Maintenance: Similar to most other dams, the edges need to be kept clean, it is good to get a perennial ground cover growing around the edges. Our choice here in the subtropics is pinto peanut, a perennial prostrate ground cover legume, but any other perennial ground cover gives you a carpet style cover for a clean edge to the dam, making it easier to maintain, feed and harvest your fish. This goes for spill ways too, they need to kept clean and open so they don’t clog and cause problems in large rain events. One thing that is a little bit different with a fishpond, compared to a regular dam, is the amount of nitrite in the water and thus the abundance in life encouraged and enhanced, creating a faster build up of anaerobic material converted to soil on the bottom of the dam, which needs to be maintained every few years. Perhaps every 5-10 years you will need to drain the pond and remove the nutrient rich soil, laid out to dry and used as a top-dress fertiliser on gardens and fruit trees. It will naturally convert from anaerobic to aerobic soil when it is dried out, or it could be used in compost as an enhancing agent as food for aerobic organisms. In a highly a productive aquaculture system, you can manage to get 1 kg of fish produced in 1 cubic meter of water.

The fishpond in the photo is roughly 800 cubic metres of water which is approximately 800 kgs of fish we can harvest within 18 months.

Happy fish-ponding!

Further Reading:

Geoff Lawton

Geoff Lawton is a world renowned Permaculture consultant, designer and teacher. He first took his Permaculture Design Certificate (PDC) Course in 1983 with Bill Mollison the founder of Permaculture. Geoff has undertaken thousands of jobs teaching, consulting, designing, administering and implementing, in 6 continents and close to 50 countries around the world. Clients have included private individuals, groups, communities, governments, aid organizations, non-government organisations and multinational companies under the not-for-profit organisation. In 1996 Geoff was accredited with the Permaculture Community Services Award by the Permaculture movement for services in Australia and around the world. Geoff's official website is GeoffLawtonOnline.com. Geoff's Facebook profile can be found here.

28 Comments

  1. Geoff,

    Where is this dam on your property? It would be really neat to have a google earth aerial showing the location of the new dam so that I can continue to live vicariously through you from cold Calgary! :)

    Thanks

    robo

  2. This dam is just below the 2 dams called “Tinkers Bubble” and “Pinchins Puddle” that are connected by the large top swale.

  3. hey rob below the main swale at top of farm , directly below tinkers bubble/ middel dam south west end of farm
    hope this helps take care mate

  4. If I were to create a pond in a hillside slope at the level valley floor, 4M deep, how wide would the dam have to be at it’s base?

    I realise I don’t need 4M deep, but if I can raise a catchment level by 4M I can gravity feed my raised bed area – it would effectively be a 4M deep pond with the bottom 2M filled in :^) I can still get round it without a pond if the dam needs to be too big with an old sink or something at the point of the spring (which is 4M up) but thought a pond would be nice too :)

  5. Hey Geoff,

    Great article. I really enjoyed watching this dam take shape during the internship. I was so inspired that me and another former student of yours (Jake Bucy) put in a dam similar to this one at the top of my property. We followed all of the directions that you mentioned in this article accept that it is a main water catchment area.

    I’m currently catching water off our our driveway and the road and directing it to the dam. I’m going to set up a gravel bed that is about 10 m long on each side going into the pond that will be planted with reed plants to act as a pre-filter. Is that enough to clean out contaminants that may be coming off of the road? or should I abandon this idea and redirect the water to a lower swale? It’s not imperative that I use the runoff water to fill the pond.

    I did some calculations and found that our geothermal heat pump uses nearly 1 million gallons a year. That water is being sent to the new pond. It is around 50,000 gal so it would fill many times a year without the additional runoff from the catchment area.

    Thanks for all of the great work that you have done and are doing. You are an inspiration to many, many people. My life has taken a very different and more positive direction since I spent those three months at zaytuna. And congratulations on the Humanitarian Water and Food Award for the Jordan project! Well deserved.

    1. Hey Dave, in my humble opinion, if you can get that road runoff water into the dam, that would be perfect and redirect it if there is no need.Regarding filtration, not only Reed beds, but with biochar and mycofiltration beds (Wine caps, oyster, elm oyster or psilocybin mushrooms do a pretty good job, eh!) would be an addition. Each important function supported by many elements…
      Much Love :::)

  6. “In a highly a productive aquaculture system, you can manage to get 1 kg of fish produced in 1 cubic meter of water.”

    Wow! This is something better than aquaculture salmon, for every kilo of salmon produced it’s used 2.5 kilos of wild fish. For example, in Norway there was in 2007 used 100000 tons of superb mackerel for fodder, as salmon aquaculture paid a higher price than if it was used directly for humans. In 2007 the production of aquaculture fish in Norway was 830,000 tons, but they were eating about 2.5 million tons of wild fish.

    “Trees such as mulberries can be established around the pond to attract insects which fall into the pond, an ancient Chinese method.”

    I wish the Chinese could have stayed with their traditions, rather than flying in huge amounts of Norwegian aquaculture salmon. As if there was not used enough oil capturing small fish out of the ecosystems for fodder, they maybe use even more oil for the airborne transport of fresh salmon for the Chinese and Japanese market. Also our government uses a lot of money marketing Norwegian salmon for the Chinese market, which they look at as highly lucrative market to make a “profit” of aquaculture salmon.

    This in strong contradiction of this system by Geoff Lawton, which produces a yield from a natural abundance, which is profitable for life!

    Still the Norwegian aquaculture industry say their product is a sustainable one, within the carrying boundaries of nature. I guess they need to take a trip to Zaytuna farm, taking a look at Geoff’s fish pond and having a good talk with Geoff. Hopefully they should change their mind?

  7. Many thanks Geoff, I just happened to have a piece of squared paper handy when I read your post, it’s all sunk in! I can’t wait to get the bunyip out an see if it’s really doable :)

  8. Great article Geoff

    Assuming that someone has almost no clay content on their property, what suggestions are there for dams and ponds? Are concrete or synthetic/plastic linings frowned upon?

  9. If I were to extend the theoretical dam in my post above with a swale, and the hillside is already 3:1, what is the maximum angle of the uphill swale wall? I’m working on 45degrees to give a depth and width of 1M, but I could make it a little shallower angle by widening the uphill side if necessary.

  10. Hello, i was wondering is it a good idea to put tyres in our dam so the fish can hide in them, or would they be toxic to the water. and also i have no idea how or what plants to put in i cannot put any plants around the outside because the dam evaporates during summer so i don’t know how to get plants in the middle the dam is over 10 years old now and has lots of yabbies to feed fish Hope you can help Many thanks Breeta

  11. Pete if you have a very low clay content you could do some small scale trials with bentonite or some of the new dam sealing polymers. If you have animals like cows you could try animal compaction with manure gley. Start small and see if you can seal some small ponds first.

    If you cannot find a cheap way then a plastic liner or concrete maybe you only way.

  12. Hi Breeta clay pipes or even concrete pipe rejects would be better.
    Source your water plants from ponds and dams near by or as close as possible with good looking healthy water and choose plants that are not too rampant, good looking and go for diversity. Plant underwater by just sticking them into the mud in the same depth you pull them out from and it usually works good.

  13. We live 100k north of Perth in WA and have four small dams, all plastic lined as we live in a sandy limestone area(we tried the bentonite – YUK) the dams are approx 20m x 40m but freeform and look great, they are stocked with Silver Perch, my question is.. how to harvest the big ones without harming them – I have someone wishing to stock their new dam with some BIG fish. However my fish are well fed and the minute we try to net some they all disappear for a week or two. Has anyone heard of and/or tried a solution of ‘oil of cloves’ and if so – any idea how much to apply?

  14. Hi,
    We are just this week in the process of clearing a 60 meter wide 4 meter deep dam, ready for the plastic liner to go in shortly after (B****Y thing never held water).
    All the slopes are reasonably steep, and i am wondering if the lack of vegetation growing on the edges will have an adverse effect on any fish that we put in? To be honest we haven’t really looked into this side of things, but i guess we are hoping to have fish reproducing etc…
    Can anyone point me to an expert on this matter to talk to?
    Thanks

  15. Help needed.
    I am in Cambodia at Siem Reap and trying to help a Street Kids project – Green Gecko repair their fish pond/lake.
    They have already built it with straight sides, put a fence around it to stop fish escaping during the floods. We need to make the sides higher in the hope of getting rid of the fence however, I am not sure there is the material to do it. There are 2 main people involved – one would like a clay/soil sided dam and the other thinks the best way is to concrete up the sides.
    Problem – I think the concrete will slowly fall into the water side of the dam – especially if we put soil on the outside to plant into. also am not sure of the footings already there.
    The property is already flood prone due to low lying ground and there is not enough soil to move from outside the pond area.

    any ideas? please
    I can send some photos.

  16. Iam in Zimbabwe and have managed to find some helpful hints through your website. I want to start a fish rearing business so please be free to send and vital information to my email address. Keep up the good work.

  17. The biggest dam on our property is about 5 megalitres. I put 20 rainbow trout fingerlings 7′ in. Harvested about five well over plate size about 2 yrs later. This time around put 40 5″ fingerlings in approx. 1Yr later no sign of trout. Not rising to pellets. I believe Cormorants have taken ’em all. Thinking of submerging a stack of Forklift Pallets to create a hide. What do you think? I know Cormorants are a problem world wide.

  18. I have a dam on new property (looks healthy) and am stocking with some yabbies (for fun). I am wondering how best to care for the yabbies (so they stay alive and grow(!) and wonder whether they will eat the waterlilies, I am also hoping to add.

    1. Yabbies can be fed bits of carrot, Oats and stuff. Don’t think they will eat waterlilies, they often eat each other. Search on Yabbies you should get lots of info.

      1. Keep it up for giving me the technology on fish pond construction. I would like to learn more. Am in Malawi working as a pesant farmer

  19. I am planning to establish a trout pond in an area about the size of three average swimming pools, 1.2m average depth- flat bottom- irregular shape. The ground in Childers Victoria is very pourus (ideal for potato growing). Do I seal the dugout with plastic ? or do you have another solution. Costs ? Photos available if required. Thank you. IDM

  20. Hi,

    This is very wonderful and indeed useful information.

    I have one question:

    Can I construct a fish pond at any place including a dry area or should a fish pond only be constructed in a dump, swampy, wed area?

    I ask this question because my piece of land is at a dry area but I intend to sink a borehole which may go about 60-70 meters deep. My plan is to use the borehole to supply the water for the pond. Could this be a good idea?

    Thanking you in advance

    Regards
    Muzumara

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