Detailed information on physical-chemical parameters of water and phytoplankton development were first obtained for the Yana, a large Arctic river. Original data obtained comprise 181 species and varieties of algae new for the Yana flora and 17 for the Yakutia water bodies in general. Main factors limiting the development of plankton algae of the Yana were established. Integrated assessment of the river water quality according to bioindicative characteristics of planktonic algae and hydrochemical parameters was made. The obtained data are background and will use as the basis for the river ecosystem biomonitoring.