The most important water quality indicators for the Tansa Lake, namely dissolved oxygen (DO), chemical oxygen demand (COD_Cr), biochemical oxygen demand (BOD₅), ammonia, nitrites, nitrates, total nitrogen, orthophosphate, total phosphorus, chlorophyll “a”, fixed residue, total suspended matter, chloride, sulphate, calcium, magnesium and detergents were analysed in order to achieve a geochemical evaluation and classification of water quality. The alkaline character of the water from the Tansa Lake was given by the pH values that ranged from 8.3 to 8.6, these being measured in the middle lake section in May, August and November 2010. Trace elements, namely Cd, Cr, Cu, Ni, Pb and Zn were analysed using Atomic Absorption Spectroscopy (AAS). The mean values of these do not exceed the limits of the 1^st quality class of the water (Cd - 0.3 μg/L, Cr - 20 μg/L, Cu - 18 μg/L, Ni - 9.5 μg/L, Pb - 3.3 μg/L, Zn - 76 μg/L). In agreement with the current Romanian legislation and the Water Framework Directive - 60/2000/EC, the water quality classes were established. The overall water quality of the Tansa Lake fits into the 2^nd quality class. This means that the water can be considered as being in a “good state”, but not suitable for drinking purpose. The Tansa Lake belongs to the hypertrophic lake category, in accordance with the analysis of the trophicity degree (total nitrogen - N, 1.11 to 1.23 mg N/L; total phosphorus – P, 0.05 to 0.21 mg P/L and chlorophyll "a", 8 to 36 μg/L).