| Summary: | The paper presents the changes that have occurred in the morphometry of Lakes Gopło and Ostrowskie, which are located
in central Poland. The analysis covered the period characterised by increased human interference into the water cycle, which has
been taking place continually since the mid-eighteenth century. On the basis of available cartographic materials (aerial photographs,
topographic maps, bathymetric charts of the lakes) and the authors’ own field measurements digital terrain models were developed
for the immediate environment of the surveyed lakes. These models, in turn, were used for measuring basic parameters characterising
the external dimensions of the lakes (surface area, length and maximum width, shoreline length) and their underwater relief (volume,
maximum and average depth). In addition, the selected indicators of the shape and form of the lake basins were determined. The results
showed a drastic reduction of water resources of the two lakes. The basin of Lake Gopło covers only the deepest parts of the former
reservoir, accounting for only 23.3% of the lake before 1772, and 32.5% of its former volume. In the case of Lake Ostrowskie the surface
area and volume decreased, respectively, by 23.5% (74.9 ha) and 21.3% (6 695 000 m3). Such large changes in surface area and volume of
both lakes have contributed to significant changes in other morphometric parameters and indicators. In particular, significant changes
were observed in relation to such morphometric characteristics as length and maximum width, as well as average and maximum depth.
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