The altimetric and granulommetric proofs, as well as their shape, include them in the category of typical fluviatile limans from this point of view. The four analysed lakes contain fresh water with a higher mineralization than the Danube. The increase of concentration corresponds to the periods in which the connection with the river is interrupted. The marshes Vederoasa and Iortmac have a higher salt content due to underground supply. Due to its chemical properties, the water of all marshes are included in the class of bicarbonated waters – calcium group, when they are supplied by the Danube, or sodium group, when the connection with the river is interrupted and a chemical metamorphosis process takes place (Bugeac, Oltina, Dunareni marshes), or magnesium group when water supply comes from own sources (Vederoasa, Iortmac and Baciu marshes). The structure of vegetation in the lacustrine cuvettes included five aquatic associations and four swamp associations. The lakes vegetation cover degree has percentages between 10-90%. The greatest plankton amount is found at the junction between the lakes and the supply channels coming from the Danube. The reduced species diversity reflects the answer of the fish population to the changes of the environmental conditions.