One of the most important elements in the protection of water quality is buffer zones. In order to protect water quality, appropriate management of these areas is necessary. In the paper, changes in the land use in the buffer zone of 200 m width around lakes in the Mała Wełna catchment over 20 years were analysed. For the study eight lakes larger than 50 ha were chosen. Changes in the land use within the buffer zone were studied from 1980 to 2000, based on topographic maps in the scale 1:10 000. Results show both positive and negative aspects of land changes. An increase in forested areas and grasslands through tilled land were positive aspects of these changes. On the other hand, the enhancement of suburban development in these zones caused increased probability of water pollution from these areas. Calculations of potential nutrient loading from different types of land use in these zones indicated an enhancement of nutrient sources in the lakes within the 20-year study period. However, these changes are not significant in comparison to the nutrient loads contributed by the tributaries. Our study indicated that in the case of flow lakes, more important is an improvement in water quality in the tributaries and a reduction in nutrient sources in the catchment with the purpose of reducing the input of nutrients into the lake. Management of the buffer zone is one of the issues which have to be taken into consideration in lake protection after elimination of the major water pollutant sources.