Earthen bottom ponds have several advantages. They are relatively simple to build, inexpensive per unit of surface area, and if well constructed, of low maintenance and usually long lasting. However, there are many drawbacks to these ponds that make them a less advisable choice. Earthen bottom ponds require a great deal of land as small earthen ponds do not maintain themselves well. Small natural ponds never clear properly due to the slow but invariable dissolution of soil into the water and the difficulty of underwater shelf construction with clay soils. In addition, any of the natural occurrences such as moles and insects digging into the pond will have a greater effect on smaller ponds. Most plants in earthen ponds are planted directly into the soil, as plant roots often creep over the edge of pots and escape. Once out of the pot, most aquatic plants become very aggressive with their spread being checked only by water depth. For these reasons, earthen bottom ponds, especially small ones, are not recommended.
If the decision is made to build an earthen pond, the soil must have a relatively high clay content which makes the soil more difficult to work. Due to the required size and land needed, they are more expensive per pond. Plants in them are prone to grow more vegetatively and flower less. Plants, fish, and other wildlife are harder to maintain. Unwanted guests to the pond will be more common and much harder to control. The water may often be muddy in appearance. If fish are included in the pond, they will keep the water muddied as they forage on the bottom.
The basic construction of earthen bottom ponds starts with size and shape designs. Once these factors are determined, remove the soil plus 6 inches for relining. Bring back onto the site enough of the heaviest (highest clay content) soil that you have and line the bottom and sides with a 6 inch layer. This soil must be wetted as it is returned and rolled until all of the structure is broken down and the soil becomes slick. This is called “puddling” the soil and creates a layer almost impervious to water. Then wait for enough rain to fill the pond before planting.