With the growth of large-scale, confined, commercial animal systems in the United States, management of the ensuing livestock waste has become a major source of environmental concern. For the swine industry, this waste is typically treated in large anaerobic lagoons. However, high levels of ammonia (NH₃) may escape into the atmosphere by volatilization. Its subsequent deposition across the surrounding landscape can be a significant source of nitrogen non-point pollution in these areas. Biological removal of ammonia via nitrification is therefore a critical and often rate-limiting step in the removal of nitrogen as N₂ through biological nitrification/denitrification systems. The discovery of bacterial populations capable of efficiently nitrifying high levels of ammonia at cold temperature represents a tremendous benefit to on-farm wastewater treatment systems. This study describes the identification and characterization of such bacterial populations.