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The optical properties of the ice and water columns of lakes of the McMurdo Dry Valleys are described. Attenuation of light is dominated by the effects of the permanent ice cover, which reduces incident irradiance between 78 and 99%. The ice cover also imparts a strong blue to blue‐green bias to its spectral distribution. Attenuation by ice can be highly variable over short time and distance scales. This is related to the nature of incident light (direct or diffuse), ice temperature (which affects crystal structure), snow cover, solar angle, and the amount of sediment and air spaces within the ice. Transmission is highest in ice at low temperature, with diffuse incident irradiance, in the absence of snow and at low sediment and bubble contents. Within the water columns, most attenuation is due to water itself. The lakes typically have extremely low concentrations of dissolved yellow substances. In some strata, phytoplankton …