There are results of water quality assessment of Yalpuch lake – Bolhgrad town to trophic saprogenous biological criteria and specific substances of toxic effects for the period 1951-2013, divided into 11 short periods of time and the phases of the water regime. Index of water pollution and overall assessment of water for the whole set of parameters (the so-called degree function R) was calculated. In general, the northern part of the lake water is moderately polluted under significant anthropogenic impact which level is close to the limit of stability of the ecosystem.
Key words: water temperature, transparency, acid capacity, nutrients, biological and chemical oxygen demand, index of water pollution, heavy metals and elements.