Most ponds lose some water due to leaks, and it's not uncommon for the water level in ponds to fall in the summer or during times of drought. However, the Missouri Department of Conservation says if your pond is chronically low, then you may have a problem that needs attention.
The most common cause of pond leaks is tree roots penetrating the dam.
Cutting large trees isn't wise, since decaying roots leave fissures through which water can escape. Instead, prevent the problem from worsening by cutting all trees less than 3 inches in diameter and repeat the procedure as often as necessary to prevent new trees from growing.
Improper dam construction is the other major cause of leaks. Usually the problem is that the soil in the dam or the bottom of the pond is too porous. If the dam is the problem, the surest cure is rebuilding the dam.
However, leaky dams and pond bottoms sometimes can be fixed by applying bentonite. This is a special clay that expands to twice its dry volume when wet, sealing holes.
Bentonite is used in drilling and is available from drilling supply companies or farm co-ops. It can be used several different ways, which are outlined in "The Problem of Leaky Ponds." Information about designing and maintaining ponds to prevent leakage can be found in the "Missouri Pond Handbook," another Conservation Department publication.
These publications are available on request from Conservation Department regional offices or by writing to Distribution Center, Missouri Department of Conservation, P.O. Box 180, Jefferson City, MO 65102-0180.