A quartz prism dispersing system in a specially designed housing was used for evaluating the intensities of different wave-lengths in the visible spectrum at different depths in vater on Gunflint Lake on the northern border of Minnesota. The spectrum was photographed at different points down to 70 ft. and from these the intensities of the different wave-lengths were evaluated from characteristic curves obtained from standard exposures by using wire creens. It was found that the variation of the intensity with depth was exponential in the case of some wavelengths but not in the case of all. From the results obtained, absorption constants were obtained for the different wave-lengths.