In the West Siberian Plain, for a 90-year period Elodea сanadensis has spread initially from the forest-steppe part of the Transurals (the Tobol River basin) mainly along the valleys of large rivers and their feeders as well as in freshwater objects in dividing areas up to Surgut (6'°'9N, 73°24'E) in the north and Ekibastuz (52°0'N, 75°22'E) in the south. The authors have found populations of Е. canadensis in 32 of the 640 studied water bodies (5%), including '4 in Tyumen Region (4 of them in the Khanty-Mansijsk Autonomous District), '2 in Omsk Region, 6 in the northern part of the Republic of Kazakhstan. In the covered territory, the invasion species E. сanadensis exhibits dominating behavior and displaces indigenous species of immersed hydromacrophytes (Ceratophyllum demersum, Myriophyllum spicatum, Potamogeton crispus, P. friesii, Hydrilla verticillata) from the hydroecotopes. The average projective cover by E. сanadensis in the studied West Siberian coenoses is up to 52%. Projective cover by E. сanadensis over 80% has been registered in more than 30% coenoses where this species occurs. In the forest-steppe botanical-geographical belt, coenoses with dominating E. сanadensis form a wetphytomass in the amount up to 3 700-7 336 g/m 2, which is equivalent to 368-690 g/m 2 of air-dry weight. Today, the trend towards further spreading of E. сanadensis across the West Siberian Plain remains.

The author gives short description of the explored territory's water objects at the beginning of the article. He cites the classification of lakes of the Tara River Valley on the basis of the factual and his own data. The author comes to a conclusion that the majority of the explored lakes are the old bed areas of the Tara River. Continuing the description of the explored territory's water objects the author gives hydro-chemical characteristics of their water using his own data. Concluding the description of the explored territory, the author gives details about the most common organic and inorganic sediment types in water objects. The main body of the article is devoted to the exploration results of the flora and cenosis composition of the vegetation cover of the Tara River Valley water objects. The author presents information about new locations of water macrophytes rare species and about new locations of species included in the Red Book of Omsk Region. The description of partial activity of macrophytes species in the explored territory's water objects was introduced. The result of the exploration was finding a new species of macroscopic alga for Omsk region Chara braunii. According to the data of geobotanical descriptions the list of water macrophyte groupings types for the Tara River Valley water objects was made. The author emphasizes that the mentioned groupings types are habitual in the lakes of the Tara River Valley. The mentioned groupings in many cases occupy sizable water areas. The information about the most rare communities in the presence of Hydrilla verticillata was introduced. In the conclusion the author cites information about the rate of trophicity and saprobity of the explored water objects on the basis of the data on the species composition and the cenotic structure of their vegetation cover. The flora basis of the Tara River and the valley lakes is composed of mesotrophic and mesoeutrophic species. The common mesotrophic character of the flora points at medium biogenic elements content in the water ecosystems of the explored territory. The estimation of water organic pollution or saprobity demonstrated that fairly pure water predominated in the explored territory's water objects.