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Abstract
Druzno Lake is the semi-natural, hypertrophic basin located ontheZuawy polders (delta of Vistula). The area is13-29 km^sup 2^, with mean depth of 1.25 m. The lake isextremelypolymictic and of throughflow character: the water retentiontimeis very short (20 days!). Almost 90% of the bottom isovergrown bymacrophytes. The productivity, especially of phytoplankton, isveryhigh. The main factors of ecosystem stability are:There are very good oxygen conditions in the lake. Organicmatterundergoes quick mineralization. Due to often resuspension andintensive throughflow a considerable part of the mineral andorganic seston is 'exported' out of the lake.By dredging the navigable channel, additional amounts ofsuspendedmatter have been exported out of system. Therefore thesetechnicaltreatments slow down the processes of shallowing and aging ofthelake and support lake's existence.[PUBLICATION ABSTRACT]