Stop Fish Escaping Ponds in Floods: 3 Simple Barriers

When heavy rain lifts your pond above its banks, tilapia, catfish, carp and other fish swim out with the water and are gone in one night. If you want to stop fish escaping pond flood water, you need a barrier that stands higher than the water and lets water pass but keeps fish in. This guide shows three simple barriers: nets, bamboo fencing and raised pond walls. You can use one, or combine them for the strongest result. Build them now, while the rain is heavy, on days when the pond is calm and safe to work around.

Know Where Your Pond Will Overflow

Before you build anything, walk around the pond and find the weak points. In many parts of Southeast Asia, from Cambodia and Thailand to Vietnam, Laos and Myanmar, the late weeks of the rains bring the highest water of the year. Low ponds near rivers or rice fields are most at risk.

Look for these signs:

• Low spots in the bank where water already comes close to the top.
• Places where the bank is thin, cracked or washed away.
• Inlets and outlet pipes, where fish often slip out.
• Paths where water from nearby fields runs into the pond.
• Crab or rat holes that can grow into leaks.

Push a bamboo stick into the bank at the lowest point and mark the highest water you have seen. Your barrier should stand at least 30 to 50 cm above that mark. Ask neighbours how high the water reached in past years. They often know better than any map.

Wear rubber boots with good grip and work gloves. Banks are slippery after rain. Never work alone near deep water, and do not go near the pond when water is rising fast or flowing strongly across the bank.

Barrier 1: A Net Fence Around the Bank

A net fence is the fastest barrier to build. It lets flood water flow through while holding fish inside. You need fishing net or nylon mesh, bamboo or wooden poles, and strong string or wire.

Choose the mesh size for your smallest fish. For fingerlings, use a fine mesh of about 1 cm or less. For larger fish, 2 to 3 cm mesh is usually enough. Prices vary a lot by country and quality, but nylon net often costs roughly 0.30 to 1.50 US dollars per square metre.

How to build it:

• Cut poles about 1.5 to 2 metres long. Sharpen one end with a machete, cutting away from your body. Wear gloves and eye protection.
• Push or knock the poles into the top of the bank, about 1.5 to 2 metres apart. Drive them at least 50 cm deep so the flood cannot pull them out.
• Dig a small trench about 20 to 30 cm deep along the inside of the poles.
• Tie the net to each pole, top and middle, with strong string.

Now bury the bottom of the net. Lay the lower edge of the net into the trench and fill it back with soil. Press it down hard with your boots or a tamper. Many fish, especially catfish and snakehead, will push under a net that only touches the ground. A buried edge stops this. Check that the top of the net stands well above your high-water mark.

Barrier 2: Bamboo Fencing for Stronger Banks

Net alone can sag or tear when floating branches and rubbish hit it. A bamboo fence is stronger and lasts longer. Many farmers across the region, from the Philippines to Indonesia and Malaysia, use woven bamboo or split bamboo panels around ponds and fish cages.

How to build it:

• Use mature bamboo, as thick as your wrist or more. Bamboo poles often cost about 0.50 to 2 US dollars each, depending on place and size.
• Split some bamboo into long strips, about 2 to 3 cm wide. Split away from your body, wear gloves, and keep children back. Bamboo edges are very sharp.
• Set strong main posts every 1 to 1.5 metres along the bank, driven deep into firm soil.
• Tie two or three horizontal rails across the posts with wire or rattan.
• Weave or tie the split strips upright onto the rails, with gaps smaller than your smallest fish.

For the best result, line the inside of the bamboo fence with net and bury the net edge, just like Barrier 1. The bamboo takes the force of the water and debris. The net keeps small fish in. If your area gets strong currents, add a sloping brace pole on the outside of every third or fourth post.

Barrier 3: Raise the Pond Walls

Raising the bank is the most permanent fix, but it is also the most work. It works best for small family ponds with firm clay soil. Do this work only when the pond level is stable and the ground is not flowing with water.

How to raise a wall:

• Clear grass and roots from the top of the bank so new soil can bond with the old.
• Use clay soil if you can. Sandy soil washes away fast.
• Fill sacks with soil, about two-thirds full, and tie them closed. Sandbags can cost about 0.10 to 0.50 US dollars each, but prices vary.
• Lay the sacks along the low parts of the bank like bricks, with the joints staggered.
• Press each layer down firmly before adding the next one.

Keep the raised wall wide at the base and narrower at the top, like a small dyke. A wall that is too tall and thin may collapse. Plant grass such as vetiver on the bank later to hold soil with roots. Lift heavy sacks with your legs, not your back, and share the load with a second person. Wear gloves and sturdy boots.

If your pond is large, close to a house, or the bank holds back deep water, a collapse could be dangerous. In that case, talk to an experienced local builder or agriculture extension officer before raising walls. Some areas also have rules about changing banks, ditches or drainage, so check local rules first.

Protect Inlets, Outlets and Check During Storms

Even a good fence fails if fish escape through pipes. Cover every inlet and outlet with a fine screen or net bag tied tightly with wire. A simple overflow pipe set just below the bank top, with a screen on the inside end, lets extra water leave slowly instead of pouring over the top.

After each heavy rain, walk around the pond in daylight with a second person and look for:

• Holes or tears in the net, and gaps under the buried edge.
• Leaning or loose poles.
• Rubbish, branches or water hyacinth piled against the fence.
• Wet or soft spots on the raised wall.

Remove debris with a long rake or pole from the bank. Do not wade into flood water to clear it. Moving water can knock you over, and it can hide holes, sharp objects and snakes. If you use an electric pump to lower the pond level, keep cables and plugs dry and away from water, and ask a qualified electrician to set it up. Stop all work if lightning, strong wind or fast-rising water appears.

No barrier is perfect. A very large flood can still overtop any fence. Conditions also differ by country and place: soil, rain, bank height, materials, prices and local rules all change. Start with the weakest point of your pond, combine nets with bamboo where you can, and ask an experienced fish farmer nearby what works in your area.