The water quality index (ICAcc) is a value to reflect the influence of different parameters on water quality, transforming large amounts of data into a single number, which represents the level of water quality. The ICAcc values calculated on the basis of scientific researches results from the years 2002-2021 demonstrate that the water quality in the Dniester river in the sections Otaci - Vadul lui Vodă was good (71-92%), only at Vadul lui Vodă in 2008-2009 years and the other sections (Gura Bâcului, Tighina, Olăneşti) in all the years of study the water was mostly with „medium pollution” (55-67%), and in 2008 at the Tighina city section water was in the „polluted” category (49%). Low values of ICAcc in the Dniester River in 1983-1985 years are as a consequence of the accident at the mineral fertilizer plant in the Stebnic (Ukraine) city on 15.09.1983, the pollutant continued its course in river Dniester and on the territory of the Republic of Moldova. Since October 1983 the water of the river has been much polluted, only in February 1984 the water becomes of medium pollution and from May - of good quality. The values of the river water quality index demonstrate that the floods in 2008 year did not essentially change the chemical composition of river Dniester waters from Naslavcea to Dubăsari, being of good quality (81-88%), and on the lower course the water was of medium pollution in the Vadul lui Vodă section (64%), reaching polluted in the Tiraspol section (49%).