Researches on biological productivity of aquatic ecosystems could not be complete if the role of bacterioplankton in the matter and energy flow is ignored.
In Siret river, especially at surface of water, existing a specific (autochtonous) microbiota, wich develops function of nutritive supplies, especially organic biodegradable substances.
In case of appears a supplementary nutrient sources (caused by pollution) will be changes in the quantitative and qualitative evolution of microbial population.
These aspects will be producing negative effects on water utilization in various economical and social interests or on the health of the people who living in riverside area.
The aim of this study is the establishing of the microbial pollution (indicated indirectly by total number of germs TNG) and in the same time we follow up certain ecophysiological groups of bacteria involved in substances recycling.
Microorganisms play a very important role in the cleaning process of the Siret river and in the wetlands near the main river course.
We are monitoring the microbiological indicators in two years, 2004-2006, on seasonal sample. There were collected water sample during the spring (March-April, summer (June July) autumn (October-November) and winter (January-February)
The sample station was selected to offer a significant image of development level of bacteria communities.
Water sample were analyzed by inoculation on the selective culture media. For interpreting the analyzed data it make the geometrical media for each sampling station, on season and ecophysiological bacteria group.
In the same time, it was monitoring several physico– chemical parameters: temperature T, pH of the water, oxygen.
Also, we are follow up the influence of the wetlands microbiota to river microbiota. | 
