Summary:

Restoration of rivers self-purification ability is an important part of the efforts to improve surface waters quality both in Poland and in the world. River regulation works are indifferent neither for the environment nor for the ecosystem of the river, as they change the ability of river waters self-purification. This article presents results of researches on changes of oxygenation and BZT5, as well as water temperature and pH in the hydrological year 2003/04 on regulated and unregulated parts of the Smortawa River. In the progress of the research, conditions of self-purification of the river have been assessed.