Building a Fish Pond in Ghana: Earthen and Concrete

Start with the water, not the spade

The first question to ask about a fish pond is not how deep to dig. It is how much water you can put into it, and whether that water will still be there in March. A pond is a bucket with a large mouth. Every litre it loses to evaporation, seepage and a dry source has to be replaced, and in the dry season that replacement often costs more than the fish are worth.

Common sources in Ghana are a borehole, a stream, a dam on a seasonal watercourse, and roof or ground catchment that fills during the rains. A borehole gives the most predictable supply, but you need a driller to test the yield before you commit. A stream can look generous in July and be a trickle in February. To measure what you have, pick the driest month, fill a 20 litre bucket from the source, time it with a watch, and work out litres per minute. Repeat it at a few times of day. That number tells you how much a pond can be topped up without a pump running all day.

Ask about abstraction before you connect anything. Check current requirements with the Water Resources Commission, because taking water from a stream or dam can need approval, and the rules are not the same for every source.

A jar test on the soil before you pick the site

Soil decides how much work the pond needs. A clay-rich soil holds water with a modest compacted dam. A sandy or gravelly soil leaks through the base and the banks, and you will end up lining it at a cost you did not plan for. A laboratory is not needed to learn what your soil is made of.

Dig a sample from 30 to 50 centimetres below the surface, well away from the top layer of roots and leaf litter. Break up the lumps, put a handful into a clear jar, fill it with water to about two-thirds, add a teaspoon of salt to help the particles settle, and shake it hard for a minute. Stand the jar on a flat surface and watch. The sand falls out within a minute or two. The silt settles over the next hour. The finest clay can take a day to clear. The layers tell you roughly how the soil is built. A thick, sticky clay band on top of the sand means the soil holds water well. A band of mostly sand means the site will leak.

Choose the site with the soil test in one hand and a map in the other. Avoid low spots where runoff gathers and floods in the rains, because a flooded pond loses its fish and its banks. Keep the pond away from big trees, whose roots crack the dam and whose leaves foul the water. Leave room for an access road wide enough for a tractor or a pickup to reach the outlet at harvest, and for the feed bags to come in during the rains.

Shape, depth and banks of an earthen pond

Many smallholder ponds in Ghana fall in a size range of a few hundred square metres. Smaller ponds are easier to manage, feed and harvest, and a larger one only makes sense when you have the water, the feed and the labour to match it. A rectangle is easier to net and harvest than an irregular shape, so square off the corners where you can. The table below sets out the dimensions most planners work with. Treat it as a starting frame to check with your extension officer, not as a specification for your ground.

Strip the topsoil first and set it aside. It is full of roots, seeds and organic matter, and it does not belong in the dam core. Dig the pond in the order you will need it. Start with the outlet end, because the drain depth controls everything else.

Compacting the dam and testing for leaks

The dam is where most earthen ponds leak. A dam built by tipping spoil into a heap and walking away will settle, crack and pass water along the line of the old roots. The fix is to build it in layers, each about 15 to 20 centimetres thick, moistened to just damp and compacted before the next layer goes on. Hand tamping works for small ponds. For larger ones, track the excavator back and forth over each layer, or hire a roller if your contractor has one.

Dry soil will not compact, and wet soil turns to mud under the machine. Aim for the moisture at which a handful of soil holds its shape when squeezed and breaks cleanly when you press it with a thumb. If it smears like butter, let it dry a little. If it crumbles to dust, add water and mix.

Test before you stock. Fill the pond to about half depth, mark the water level on a post or a stake, and wait one to two weeks. To separate evaporation from seepage, place a bucket with a little water in the pond, sitting on the bottom, and mark its level on the inside. If the pond drops faster than the bucket, the water is leaving through the base or the banks. Walk the outer toe of the dam after rain and look for wet patches or seepage lines. A leak found at this stage is cheap to fix with a compacted clay blanket. The same leak found after stocking means draining, catching fish and starting again.

Concrete tanks and lined ponds: when they earn their cost

Concrete makes sense on sandy, gravelly or rocky ground where earth will not hold water, on a small plot where every square metre counts, and where you need tight control over water exchange and harvest. A concrete tank is easier to drain, clean and net than a dug pond, and its walls do not slump. The trade-off is the cost of materials and skilled work, which you should price locally from current contractor quotes rather than from any figure in an article.

Concrete tanks need steel reinforcement and a footing that will not settle. Cracks in tank walls often start where reinforcement was skimped or where the base was poured onto soft fill. Ask the builder to show you the bar spacing and the mix before the pour, and to keep the surface damp for several days as it cures. Curing is not optional. Concrete that dries too fast is weak and cracks more easily.

New concrete is alkaline. Fresh cement releases lime into the water, and a high pH can stress or kill fish. Fill the tank, let it stand, then drain and refill, repeating until the water tests near neutral. A simple pH strip from a pool shop is enough for a first check, and your extension officer can confirm the reading. Plastic linings over compacted sand are another route. A liner needs protection from sharp stones and from the sun, so cover its edges and keep the banks neat.

Inlets, outlets and the drain you will use at harvest

The water works decide how easily you can run the pond. Plenty of trouble traces back to an inlet that washes the bank away, an outlet set too high to empty the pond, or no screen at all. The table below lists the parts every earthen pond should have and the mistake that costs farmers most often.

Put the outlet at the lowest point of the pond floor and check the fall with a spirit level and a string before the pipe goes in. A pipe laid flat will hold water in a dip, and you will be netting fish out of a puddle at the end of the season. Protect the outlet with a grille, and make sure the valve can be turned by one person. Harvest is a day of hard work even with good plumbing, and bad plumbing makes it a week.

Stopping erosion and washout in the rains

The first heavy storm after a new pond is built tests every decision you made. Bare earth on the banks washes into the water, muddies it and fills the bottom with silt. The cure is cover. Plant the banks with a grass that holds soil, such as vetiver, and cover any bare patches with the topsoil you stripped earlier. Plant before the rains, so the roots are established when the storms arrive. Check the banks after each big storm for rills and gullies, and fill them with compacted soil while they are small.

Divert runoff away from the pond. A cut-off drain above the dam, running around it rather than into it, keeps surface water from pouring over the banks. The spillway needs a hard surface where water leaves the pond, usually stone or a small concrete apron, so that the overflow does not cut a channel through the dam. If you cannot afford a hard spillway at first, at least make sure the overflow goes onto grass and not onto the dam face.

Reading the water with a bucket, a thermometer and your eyes

A pond talks to you every morning if you look. The colour, the smell and the behaviour of the fish all carry information. A green tint usually means plankton is growing, which is what you want, provided the fish are healthy. Brown, tea-coloured water can mean soil washing in or a heavy plankton bloom that is about to crash. A black colour and a rotten smell point to low oxygen and decaying material on the bottom, and that needs action the same day.

Fish that gather at the surface at dawn, gulp for air or hang near the inlet are short of oxygen. Stop feeding, check the inlet is flowing, and call your extension officer. A thermometer dipped at the surface and at depth shows how far the temperature varies. If you can get a dissolved oxygen meter or kit through your extension service, use it, because it turns a guess into a number. Write the readings in a book beside the pond, with the date and the weather, and read the book before you decide to feed heavily.

The fill-and-wait period before a single fish goes in

Fill the pond slowly. A rush of water from a full pipe scours the bottom and carries mud into the water column. Run the inlet at a trickle until the level is near the outlet, then open it fuller. Check the inlet screen after the first hour, and again after the first day, because screens fail quietly.

Once the pond is full, most farmers wait before they stock it. Many use animal manure for a few weeks to build natural food for the fish, and the water changes colour as the plankton grows. The poultry manure in fish ponds article explains how this works and where it goes wrong, and our poultry manure fertiliser guide covers how to handle and store the manure before it goes into the water. Do not add a large dose all at once. A heavy load of manure can use up the oxygen in a shallow pond overnight, and the fish are the first to pay for it.

Stock only when the water looks right, the temperature is steady and your first oxygen reading is safe. A pond that has been filled and left alone for two to three weeks is usually ready. Your extension officer can tell you whether your water and season call for longer.

What to ask your contractor before the excavator starts

Most pond disputes start with a verbal agreement. Put the job on paper before anyone touches the ground. Ask for the dimensions in metres, the depth at the outlet end, the slopes of the banks and the width of the bank top, all written on a plan. Ask how the dam will be compacted, in what layers and at what moisture, and whether there will be a seepage test before handover.

Ask who removes the spoil and where it goes, because a pile of spoil left by the gate can block the access road for a season. Ask for the specification of the inlet pipe, the outlet pipe, the valve and the screen, with the sizes in millimetres. Agree a payment schedule tied to finished milestones, such as the completed dam, the passed seepage test and the finished outlet, rather than paying the full sum at the start. Get current quotes from more than one contractor and compare the work, not only the total. Check current local rates yourself, since we do not publish prices for pond construction.

A good contractor will welcome these questions. A contractor who resists them is telling you how the job will go.

Permits and who to call before you dig

Before the first load of soil moves, make a short list of the bodies that may have a say. The Fisheries Commission can tell you what registration or guidance applies to your pond, and your district fisheries officer is the first person to visit. The district assembly handles building and land use matters on your plot. If you plan to take water from a stream or dam, ask the Water Resources Commission what approval applies. For larger projects, ask the Environmental Protection Agency whether a permit is needed. Check current terms with each body, because requirements change and depend on the size and location of the project.

Land is the other question. Get written consent from the landowner, and if the land is held by a family or a community, make sure everyone with a claim to it has agreed. A pond built on land you do not fully control is a risk you will carry for the life of the pond.

Timing the build around the rains and the Harmattan

The build has two halves that want different weather. Digging goes best when the soil is dry enough to carry the machine without sinking. Compaction, however, needs moisture, and dust is the enemy of a good dam. The practical answer is to do the tests and the design in the dry months, dig at the turn from dry to rainy season, and fill the pond with the first sustained rains.

A simple sequence that many farmers follow goes like this. In the dry months, test the water, run the jar test and agree the plan on paper. At the start of the rains, dig, build the dam in damp layers and plant the banks. Through the rains, fill the pond and watch the level for seepage. In the early dry months, let the water settle, build the plankton and carry out the first oxygen checks. Stocking follows once the water is right, and a pond built this way is ready for its first season rather than racing the weather.

Ready-to-stock checklist for the new pond

Use this list on the day before stocking. If any line is unticked, wait. A few more days in the pond costs far less than a few weeks of losses.

1. The water supply has been measured in the driest month and covers the top-up needs of the pond.
2. The dam was built in damp layers, and the seepage test has shown no unexplained loss.
3. The outlet sits at the lowest point, with a working valve and a screen.
4. The inlet screen is intact, and the runoff ditch carries water past the banks rather than over them.
5. The banks are planted or covered, and the spillway has a hard surface where the water leaves.
6. Any concrete has cured and been flushed, and the pH reads near neutral.
7. The water is coloured with plankton, the temperature is steady and the first oxygen reading is safe.
8. Your extension officer has seen the pond and agreed the stocking plan.

For the species side of the decision, read our starter guides to tilapia farming and catfish farming, and for the money side, the planning steps in our poultry business plan apply to a fish pond as well. Keeping fish next to birds is a farm-design question too, and our integrating poultry, crops and fish article looks at how the pieces fit. If you run birds as well, day-old chicks can be ordered through our order form, and partner with us explains how farms work with the hatchery. If the bird side needs a hand, the number is +233 24 915 1503 on WhatsApp.

Questions farmers ask