Our paper reports the phyto- and zooplankton changes studied in Lake Uzarzewskie in 2010-12 under the influence of a restoration procedure. It is a small (10.6 ha), not deep (up to 7.3 m) but thermally stratified, natural, kettle-shaped lake fed with waters from the Cybina River. Water of the tributary rich in nutrients was responsible for the hypertrophic state of the lake. To improve the condition of the lake, some restoration measures were applied. They included the iron treatment method used for phosphorus inactivation. The second method used for the lake restoration was transport of the water rich in nitrates flowing from the springs at the bottom of the slope near the lake by special pipes to the deepest part of the lake, to increase the redox potential at the sediments-water interface. The most abundant group of phytoplankton were cyanobacteria, (especially in summer and autumn months), diatoms, cryptophytes, and chrysophytes. Chlorophytes were the most numerous in respect to the number of taxa. The most important taxa were Planktothrix agardhii, Aphanizomenon gracile, Pseudanabaena limnetica, Limnothrix redekei, Cyclotella, Stephanodiscus, Rhodomonas lacustris, Cryptomonas marssonii, and C. reflexa. Comparing with mean abundance and biomass of phytoplankton in 2010, a small statistically significant decrease was noted in 2011, but an increase in 2012. Some improvement in water quality judged by Shannon-Weaver diversity index and species composition, abundance, and biomass in the lake plankton was observed. Zooplankton was dominated by rotifers. Among cladocerans the most abundant were Bosmina longirostris and Eubosmina coregoni, which were not effective enough in phytoplankton control.
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