Sealing fish ponds

Fishing

Few farmers use aquaculture in Latin America, though it could have great potential there. One of the reasons is that the soils are often too porous – they do not hold water well. It is possible to make artificial linings – using polyethylene or rubber sheets or cement. However, these methods are expensive.

Gleying

There is one way of sealing ponds which does not cost anything. It is not a new method – it was first used in Russia, but has been rediscovered and adapted.

  • Dig the pond and compact the soil really well.
  • Clear the pond of stones and rocks.
  • Cover the bottom and sides with a thick layer (2–3cm) of fresh manure – pig manure is best.
  • Cover the manure with a layer of fresh grass cuttings or fine chopped leaves (eg: bananas).
  • Add a layer of soil and press down firmly all over. You can use your feet to compact the layers. The soil keeps out the air and allows a biological process known as ‘gleying’ to take place.
  • Leave to dry for 2–3 weeks without disturbing the layers. Do not try this during the rainy season.

After 2–3 weeks, fill the pond with water. Tests using this method have been tried with great success in Costa Rica and on sandy soil at ECHO in Florida, US.

You will need to be careful not to disturb the bottom of the pond too much by scooping out the bottom mud, walking or stirring with sticks. Try this method first on a small pond.

Clay lining

Another ‘traditional’ method of waterproofing a pond was used many hundreds of years ago in the UK. Dew ponds were built on the chalk downs which normally hold no water at all.

  • The pond site is prepared as above.
  • A thick covering (2–4cm) of lime is added to prevent damage by earthworms.
  • Heavy clay is then dug and carried from elsewhere and puddled in with the feet – beginning work from the centre outwards. The clay layer should be at least 5–6cm thick and must be kept wet all the time.
  • As more clay is added, the centre of the pond must be kept filled with water. If the clay is allowed to dry it will crack and leak.

Hundreds of years later, many of these dew ponds are still in use for livestock.

Information on gleying from ECHO, USA and William McLarney and J Robert Hunter. Information on dew ponds from Mike Withers, Bishop