Abstract
The research involved a detailed analysis of transformations in water relations in the Wieczno Południowe (Wieczno South) lake drainage basin in central Poland, in the physical geographical region of the Chełmno Lakeland. Significant changes were identified in the water relations in the catchment, which were caused by a number of anthropogenic factors. The most significant factors include land development works, changes in land use (a decrease in wetland area in favour of arable land), and the extraction of water from Lake Wieczno South (for irrigation purposes) and the creation of a weir construction on its outflow. It has been shown that in recent years the drainage basin’s water resources have been affected by climate fluctuations manifested as an increase in sums of evaporation. As a result of the deterioration of water relations in the catchment, the hydrological type of some lakes (Płużnica, Wieczno North and Wieczno South) have changed, which unexpectedly resulted in an improvement of their water quality. Taking into account the forecasts for further climate change, this factor will probably have a decisive influence on the water relations of the studied area in the coming years.