SIO Reference 58-80. Eight important optical properties have been obtained for Lake Pend Oreille, Idaho, using the method of measurement of radiance distribution as a function of depth. The method for computing the properties from radiance distributions is given in detail. These properties are associated with a narrow band of wavelengths at 480 mu and are given for a single depth. They should be characteristic of the lake water in the absence of plankton or excess contamination.