All presented mean values for reservoir water should be classified as class I (very good state/potential)
according to legal regulations. However, high values of oxygen content in the waters of the lake are
interesting. In the summer period the waters of the reservoir in epilimnion reach the state described as
supersaturation (up to 17.65 mg O2 dm-3, which is a level similar to that found in the cold waters of Antarctic
lakes [5]). This is caused by massive production of oxygen by growing phytoplankton. Besides oxygen, CO2
is also present in lake water, which significantly influences the pH values. Growing algae take significant
amounts of CO2, at the same time causing the increase of water reaction (pH). In the reservoir there is a
gradual increase in this parameter, starting from values near 7 in the winter period up to maximum values in
the summer period (pH = 9.9). Such high pH values provide conditions for the biomass to grow, what is
indicated by high concentrations of chlorophyll in the waters of the lake in August 2010 (90.25