Factors affecting the optical properties and water clarity of Lake Ellesmere were investigated over an 18‐month period. The dominant cause of light attenuation was scattering. Clarity was found to be more dependent on very high levels of inorganic suspensoids than on phytoplankton biomass; however, high levels of chlorophyllawere also present. Fluctuations in inorganic suspensoid levels could be explained by different wind velocities before sampling. Wind velocity is thus one of several parameters that could be used to monitor the degree of light attenuation in this lake. The very compressed euphotic zone explained why macrophyte growth was restricted to shallow and/or sheltered embayments.