The restoration of the anthropogenic Pławniowice water reservoir with the hypolimnion withdrawal method (the Olszewski's tube) began in December 2003. The decision to restore the reservoir had been taken due to its terrible condition resulting from the hypertrophy, which had been indicated by the research from the years 1993–1998.

The following paper presents the results of eight-year-long research into the formation of oxygen conditions and restoration settings. They were compared with the data obtained from the research before the restoration. Positive changes were witnessed. It was showed that grasping the changes in oxygen conditions enables the comparison of oxygen profiles in the same months in subsequent years. The ratio of anoxic water layer thickness to the oxygenated layer thickness was suggested as a factor characterizing oxygen conditions. The area described with an izooxa in the xy coordinate system was suggested as a factor [O2 mg/m2] allowing researchers to understand and describe occurring changes. It was observed that the oxygen solved in water as a result of the restoration occurred in the whole water column in the third decade of July. The oxygen concentration in the hypolimnion gradually rose in May, June and July each year. It was showed that the improvement in oxygen conditions stemmed from progressing oligotrophy of the reservoir.

The research was conducted in a relatively small (26.8 ha) but quite deep (17.3 m) Lake Długie in Olsztyn, Poland. For over 20 years the lake was collecting sewage which eventually caused its complete degradation. In 1987-2000 the lake was restored using the artificial aeration method with destratification of water. The results showed that the artificial aeration effectively limited the internal loading. Application of this restoration method resulted in reduction of phosphorus compounds concentrations in the analyzed water strata. The decrease of TP in bottom sediments (to the level of 3-4 mg P g·' DW) was probably associated with the fact that a new layer of sediments was created, reflecting a change in the aquatic conditions caused by the restoration. The investigations conducted in the reference years showed that the changes were not permanent. A high concentration of phosphorus compounds in bottom sediments, low sorptivc capacity and a tendency to oxygen deficiency, indicate that further possibility to decrease the amount of phosphorus compounds in the lake by this restoration method is limited.