This article contains laboratory findings of particle size distribution of suspended solids in water samples from a microcosm (an experimental model of a closed natural ecosystem) and lakes of Altai Krai which have become available by means of the method of optical transparency fluctuations and a measuring and computing complex. A comparison of experimental data with measurements obtained by optical microscopy, which shows their satisfactory consent, was carried out.

Key words: transparency, suspension, concentration and par-ticle size, fluctuations.