The efficiencies of the restoration of two lakes of varied morphometries and trophic states—meromictic, hypertrophic Lake Klasztorne Małe, and dimictic, eutrophic Lake Klasztorne Duże—with the use of the phosphorus inactivation method with sequential application of iron and aluminum compounds have been compared. The total dose of the agents applied for Lake Klasztorne Małe was 38 tons of PAX 18 (aluminum polychloride) and 14 tons of PIX 111 (iron chloride), and for Lake Klasztorne Duże, it was 74 tons of PAX 18 and 46 tons of PIX 111. After the application of the compounds, better efficiency of phosphate removal from the surface water layers was obtained in the case of the dimictic, eutrophic Lake Klasztorne Duże. The use of two doses of compounds did not lead to complete precipitation of phosphates from the bottom water layers of either lake. It is noteworthy that in the case of both lakes, inhibition of the internal loading process was observed. The obtained results for the Klasztorne lakes showed that the use of two types of compounds makes it possible to reduce the cost of restoration, and moreover, the dosing of iron salts in the coastal areas of the lakes ensures a higher level of ecological safety.

The research was carried out on the flow-through Lake Mielenko (7.8 ha; 1.9 m), which also acts as a stormwater receiver. In 2015, a disposal for road salts was created in the lake’s catchment area. As a result of the inflow of salt-contaminated stormwater, there was a significant increase in the concentration of calcium (57 mg Ca/L), chloride (220 mg Cl/L) and electrolytic conductivity (790 µS/cm). Increased calcium concentrations in lake waters changed their hardness from low to medium-hard. The ecological effect of the change in hydrochemical conditions in Lake Mielenko is the Potamogeton crispus that grows abundantly in this reservoir, which prefer calcium-rich water. The overall aesthetics of the lake have deteriorated significantly, and the availability of water for recreation has also been limited.

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