This paper is devoted to the study of algae belonging to the genus of Scenedesmus Meyen, family of Scenedesmaceae , class of Chlorophyceae , phylum of Chlorophyta , and assesses the dynamics of species richness and its development in equivalent to 1 liter of water. The researchers consider the environmental conditions for the development of algae and its spread along the Vakh River, including horizontal and vertical river stations. The paper contains the materials on the ecological and geographical characteristics of the species. The authors have taken into account the materials of the sampling conducted in the river in August 1989 and present the results of phytoplankton study conducted at the river estuary 600 m from the river’s fall into the Ob River during summer and autumn season of 2005-2006. The discussion is based on the year-round research of 2005-2007 conducted along the entire body of the river. The data obtained as a result of observations of the estuarine vertical river station conducted July 10, 2011, are of particular scientific interest. The researchers have used classical algology methods for the study [5, 12]. According to the modern taxonomic data [20], there are 14 intraspecific taxons belonging to the genus of Scenedesmus in the Vakh River. 12 species belonging to the genus of Scenedesmus were identified in the Vakh River for the first time. The algae in more than 50% of the samples belong to the species of Scenedesmus acuminatus , S. apiculatus , S. ellipticus and S. quadricauda . The following species are considered rare algae for the river: Scenedesmus armatus , S. sempervirens , S. circumfusus var. bicaudatus , S. magnus, S. obtusus , S. parvus and S. semipulcher . Some of them were individual samples, such as Scenedesmus circumfusus var. bicaudatus , S. obtusus , S. parvus and S. semipulcher . The study has revealed a positive relationship between the increasing transparency and warmth of the river waters and the increasing species diversity of Scenedesmus genus. The greatest diversity is during the period between the end of July and the first half of August. The most growing algae are Scenedesmus apiculatus , S. ellipticus and S. quadricauda . Scenedesmus quadricauda plays an important role in shaping the overall abundance and biomass in early May, reaching its growing peak in mid-July - early August (with temperature range of 19.8-23.3ºC) and ending its growing season in the first week of December. This species usually dominates the summer-autumn period, ranking third in size in the dominant complex of the plankton in the Vakh River. The horizontal distribution has revealed that the amount of algae was the highest in the conditions of the left bottomland flow of the river estuary and complied with the highest values of algae amount per 1 liter, surpassing the number of algae cells identified at the right bank of the river, whereas the amount of algae in the wake was the lowest.