The World Health Organization included arsenic, cadmium, mercury, lead and other metals in the list of most dangerous toxic elements, which mandatory shall be monitored in the living environment. A range of microelements was investigated in the waters of the Prut River and Costesti-Stinca reservoir in 2013-2014, by using atomic absorption spectrophotometry and, more recently, inductively-coupled plasma spectrometry. Arsenic is one of toxic elements of first category, which even in low doses (tenths of micrograms) can have negative consequences on human health. In the past namely this metal was used for poisoning purposes. In the same time, arsenic is part of several drugs, paints, different compounds used in agriculture and medicine. To stress that in the waters of the Prut River arsenic was found practically in all analyzed samples, ranging 0.2-2.4 µg/l, such phenomenon has not being observed during past years. The concentrations of dissolved lead ranged 0.04-1.34 µg/l, what corresponded to the class of water quality I, according to the Regulation on environment quality requirements for the surface waters (2013) of the Republic of Moldova. They were much lower (at least by 3-4 times) than those found in the 80-90’ of past century, when the amount of discharged industrial waste waters was higher and the emission of lead in the air was more intense. In waters of the Republic of Moldova the concentration of dissolved nickel has a slow increasing trend. In its case the diapason of concentrations is quite large – from tenths of µg/l to 7.8 µg/l, which corresponds to the class of water quality I. Last years in the dynamics of copper and zinc – elements, which dynamics depends greatly on the usage of agrochemicals in the boundaries of river hydrographical basin – an evident trend of decrease was observed, anyway, the concentrations of dissolved copper in investigated waters during 2013-2014 have fitted to the classes I-II. Concentrations of dissolved zinc in waters of Costesti-Stinca reservoir and the Prut River oscillated between 0.8 and 34.8 µg/l, which corresponded to the classes of quality I-III. Manganese is a metal of high importance in the running of oxido-reduction processes. In about 30% of analysed cases the dynamics of dissolved forms of manganese indicated the class of water quality V. It was assumed that this metal occurs in dissolved form of heavily degradable organic compounds, because the leaps of manganese concentrations are correlated with the leaps of organic compounds, determined indirectly based on the values of chemical consumption of oxygen by chromium (CCO-Cr). The monitored microelements have a major importance in the functioning of aquatic ecosystems and despite the fact that their concentrations in investigated waters are much lower than 20 years ago, the complex monitoring of their migration routes and reveal of their role in the life of aquatic organisms shall be kept on research agenda.