Abstract
Meliorations of the Łęczna-Włodawa Lakeland have considerably determined its water relations within the last more than 200 years. The analysis of the map by Anton Mayer von Heldensfeld, so far not applied in studies on the drainage network of this lakeland, executed in the years 1801–04, revealed the drainage of the Uściwierskie Lowering already at the turn of the 18th and 19th century. This shifts the commencement of strong anthropogenic impact on this area to a considerably earlier period than was previously assumed. The lakes subject to analysis (Rotcze, Uściwierz, Bikcze, and Lakes Piaseczno and Łukie neighbouring with the Lowering) were incorporated into the drainage system in various periods. Such incorporation of a water body involved water level drawdown. The water level decreased first in Lake Bikcze, and the latest in Lake Rotcze. More detailed information on changes in the water level in the lakes of the Uściwierskie Lowering since 1882 was obtained based on calculation and on comparison with current data of measurements conducted by Rostworowski. The analysis revealed that the water level in Lakes Bikcze and Piaseczno, although fluctuating, has not changed within the last 130 years, whereas the water level in Lake Uściwierz decreased by 33 cm, and in Lake Rotcze by 90 cm.