This paper describes the use of an inertial sighting system for measuring the positions of surface water features from an aircraft. Sight angle and navigation data for any target sighted by the system operator during flight are recorded and can later be used to compute the target's position to an accuracy of about 10 m. The system makes use of a standard inertial navigation unit. The drift errors inherent in these units are corrected by making periodic sightings of reference targets. The system also has the capability of recording data from a variety of other airborne sensors. This paper describes the accuracy and limitations of the system and discusses examples of measurements of position and movement of surface water features and drogues.