Springs in karst areas may be difficult to detect. Because springs have less diurnal and annual variation of temperature than does surface water, temperature differences between such springs and other waters should be detectable by remote infrared thermal sensing. A drainage basin in western Alberta contains three large lakes which drain underground, and two of these had not been traced previously to known springs. In an attempt to locate air venting from a large known but inaccessible cave system, by using infrared line scanning from a light aircraft, a large spring discharging cold water into a lake was discovered. This probably is the outlet for the untraced waters, and had not been known previously because its flow varied seasonally and was masked by the lake.