Influence of green algae, Ulothrix zonata (Web. et Mohr), dominating the waterline zone, on the hydrochemistry of Baikal near-shore waters, including mesocosms, was investigated during 2010–2011. In May-June, we registered growth of pH values up to 9.5 and dissolved oxygen maxima up to 150% saturation, as well as drops of the biogenic element concentration in the water edge zone above the Ulothrix zonata belt compared to that of the open lake waters. Measurements of dissolved oxygen, pH, temperature, electrical conductivity were taken every three hours in the mesocosms. Experimental data showed growth of pH values up to 11.6 and dissolved oxygen up to 260 % saturation in daytime. Electrical conductivity of the water also increased that would mean that U. zonata creates conditions favourable for destruction of the rocky substratum it inhabits.