The subject of this paper is exposed-geomembrane-lined ponds whose leakage to the environment is highly undesirable. Such ponds are actually quite common in industrialized settings, and they form an important part of the operating infrastructure of many systems. Examples include process ponds for mining, leachate ponds for municipal and hazardous waste landfills, and wastewater treatment ponds for a whole host of industries and municipalities. The principles discussed in this paper could also apply to less environmentally-sensitive ponds, such as drinking water reservoirs or decorative ponds, where leakage is undesirable. The objective of this paper is to describe some important considerations related to these types of ponds for the design and maintenance of leakage control below the exposed primary liner. The proper implementation of leakage control systems cannot be overemphasized. Case histories of pond liner systems that failed due to non-existent, inadequate or poorly managed leakage control systems are presented.