Strzeszynskie Lake was formerly a slightly eutrophic(meso-eutrophic) water body. The aim of the current research was to define variables on both spatial and seasonal internal phosphorus loading from bottom sediments at five stations located in zones varying in depth, oxygenation, macrophyte presence,and uses of the neighboring catchment area. Ex situ experiments done with the use of intact bottom sediment cores have shown that the highest phosphorus release occurred in the deepest part of the lake and reached 3.6 mg P/m^2 d under anoxic conditions during summer thermal stratification. In turn, the internal loading from littoral sediments, which were well aerated all year round, was clearly lower.Furthermore, phosphorus accumulation in the bottom sediment was observed to reach a maximum of 1.45 mg P/m^2 d in autumn. A comparison of the internal loading intensity in lake zones with different land uses of the neighboring catchment area has shown slightly higher values at stations adjacent to the forest catchment area than those used for recreation. Changes in the land use of the catchment area of Strzeszynskie Lake, especially the increase in impermeable surfaces, have led to an increased inflow of external loads after heavy rains, resulting in deterioration in water quality and a delayed increase in internal loading.
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