The paper provides an outline of problems related to the influence of the Wieprz-Krzna Canal on the natural environment of the central-eastem part of the Lublin Polesie (SE Poland) illustrated by the valley of the Hanna River – a left tributary of the Bug River. Anthropogenic transformation of the hydrosphere accounts for the biggest changes in the valley and is caused by the working or the melioration system in 1960-80. Approximately 2.900 ha of swamp-peatbog aren has been turned into one-crop green land for intense agricultural use. As a result of unidirectional melioration (drainage) of the valley, hydrological conditions and, subsequently, the conditions of hydrological habitats' functioning have changed. It has led to such negative processes as the overall lowering of the groundwater level in the river valley, accelerated mineralization of organic hydrogenic soils and rotting or valley bogs. For over 10 years, gradual naturalisation processes have been observed in the Hanna River Valley, which results from the reintroduction of land management similar to the natural one. As a consequence, a new quality of the environment was established, reflected in a regenerated bogginess and "running wild" of meadows. The following objectives have been set up: defining the way of the valley management in conformity with its function (agricultural use, but at low capital absorption); rational water economy which would lake into account the exigencies of landscape protection and planning and the necessity to maintain the biodiversity in the Hanna River Valley ecosystems.