Cooling water requirements for the electric power generating industry constitute one of the major sources of thermal pollution. The work described herein presents: (1) a numerical solution of the steady state temperature field resulting from a continuous, point injection of a thermal pollutant into the turbulent-core region of a rectangular, open channel, (2) partial verification of the solution by experiments, (3) a means of extracting thermal and momentum diffusivities from temperature and velocity field measurements, and (4) a comparison of diffusivities thus obtained. Although the current work has emphasized the heat transfer problem, the techniques are also applicable to the analogous mass transfer problem.