A decade study of the hydrometeorology of Big Quill Lake in Saskatchewan, a saline prairie lake, has effectively used remote sensing to delineate groundwater inflow. The lake covers an area of 250 square kilometers with the groundwater seeping through 4 square kilometers. The salinity of the lake water forces the fresher groundwater to the surface by convection and spreads the colder groundwater by diffusion over an area of 50 square kilometers. The magnitude, source and discharge rate were determined using thermal diffusivity from data supplied by thermal infrared line scanning. Two thermal scans were made of the lake and the data extended to provide a seasonal index using LANDSAT computer compatible tapes. The seasonal thermal index was extended further using four shore-based climatological stations to provide areal evaporation using a modified Penman equation and a diffusion equation.