The paper presents the results of spectral light attenuation seasonal measurements, as well as the concentration of chlorophyll «a» at different depth of lake Krasilovskoye (Altai region) for the period of 2012−2014. Experimental data analysis is conducted with consideration of dispersion of suspended particles mixture in lake water. The coefficients of light attenuation appear to be at maximum during autumn circulation and summer stagnation of water masses, and at minimum during winter period. The calculation of light attenuation spectral coefficient at different lake depths is based on measurements of spectral transparency. Results of the calculation demonstrate maximum values for water samples taken from the bottom water layer. A tendency of chlorophyll accumulation during a vegetation season and decrease of chlorophyll concentration at winter period is revealed. The studied lake is characterized by relatively higher concentrations of chlorophyll «a» in the near-bottom layer of the lake. Particles size in water samples from the surface layer in different seasons is ranged within 0,6−7,5 micrometer in diameter, and the concentration is varied from 0,7·10⁶ to 8,3·10⁶сm^-3.